Roundwood arbor, on ledge?

I have a sort of two fold project I am working on here.  This first part is building a unique arbor for my grapes, wisteria, and whatever else I plant.  I have to figure out how to anchor it to ledge though.  Cheaply.  I am building a living fence around my lot and part of it will be the grapes.  The part where the grapes would get enough sun is also where the edge of the property is all rock.  
I would like to make this arbor interesting as well.  It will eventually be part of a reading/resting area outside our future library.  
The second part of this project is to gather and share ideas so that others can build their own version.  I will go through the ideas and build what specifically works for me, but that may not be best for you.
Here is the blog post I did with the idea that the comment section is a place for ideas:
http://homesteadhouligan.com/2017/05/01/open-discussion-project-round-wood-arbor/
Ideas are perfect here too.  I will attempt to link this from the post.
The "instructions" for the roundwood arbor:
"Other materials that can be used include anything I can scrounge for cheap or free.  The challenge is how to anchor the arbor.  I have to build on solid rock in many places.  No digging posts into the ground.  Bonus challenge is to make the arbor unique in some way."
A little about my project:
" The idea is to keep these discussions open, even after the project is done, for others to be able to go through the links and ideas for their own projects.   Once you finish a related project, you can share that in the comments too."

My comment/question is:  Are you sure you need to anchor it down?  If it's heavy enough it may stay put until the grapes and wisteria are very securely holding it down.  Or maybe a temporary anchor until the living anchors grow up it enough.  Just a thought....

I'm sure I could make sure it was heavy enough.  Stack a couple rocks around the base while the vines are growing.  Shouldn't take too long for the vines to take off.  Especially with the good compost I am giving them.

Here is what I ended up with.  A-frame resting on the mud over the ledge.  I lashed the poles together.  It did not end up being terribly sturdy.  I'm thinking about lashing tripods out of roundwood and putting them on either end to add a little support.

http://homesteadhouligan.com/2017/07/12/roundwood-a-frame-arbor/

I'm guessing it is "not sturdy" in the lenthwise direction?  Assuming that is the case, I think you might be able to fix it with a diagonal brace or two.  The brace doesn't need to be like a tripod leg at the end of the arbor.  Here's a picture since it's a bit hard to describe.  The red log is the new brace and the green circles are where you tie it.  If the brace is longer and can go all the way to the far corner, even better.  If it has to be shorter that's fine but make sure it forms a big triangle.  Two small braces (6' long) at each end would work also.  I hope this makes sense...  

I think that could work.  Just need a day without thunderstorms and I'll let you know!

I built a round pole single car garage one time and for a foundation built it on skids. It was so rugged that a few years later when I decided to move it, the whole structure was towed about a quarter mile away with my farm tractor. I am not saying you have to do that with this structure, but it is a possible option, or for other structures in the future.

Another way to anchor things to ledge, cheaply and strongly, is to use a hammer-drill to bore a hole in the ledge. Then use epoxy to secure an eye bolt into the ledge leaving it sticking up a few inches. notch out the bottom of your posts and slip them over the top of the eye bolt. Then to secure them, drive a lag bolt sideways through the post and through the head of the eye bolt. Nothing short of ten hurricane back to back with topple it over. It is a common trick for farmers who need to put in fencing on thin soil over ledge rock.

I hope to be building an outhouse in a week or two, "Uncle Johnny," but I may be trying a roundwood syructure on skids.  Just in case we have to move it ever.  I'm already dreading that project.
We condidered renting a hammer drill for this project and only decided against it because we are broke.  In the future, when we have a few projects lined up, we will end up renting one.  I will be extending the arbor at that point for sure.

I just noticed you are in Central Maine which means you are not far from me (we used to own the fields of the Common Ground Fair before it was sold to them in 1998). In any case, being a Mainer I understand broke...not just in the wallet but seemingly in every piece of equipment I own.

For renting eagle Rental in Waterville is the place to go. I know the owner and his wife and they are stand up people, incredible integrity and give a lot back to the community. But sometimes a better option is buying. I know, I know, you said broke, and trust me I understand that, and I also understand that Harbor Freight tools are mediocre at best, but sometimes for a tool that will get little use, they work well and cost as much to buy as they do to rent. I got a $40 impact wrench that way. It has lasted for years and years, and while I do not use it much, its nice sometimes when I had a stubborn bolt.

So nice to "meet" a local!  We ate going to Common Ground Fair this year for sure.  Hope to be able to set up a booth there in the next couple years...
We looked at Harbor Freight for a few tools.  We always check their ads.  Bought a coyple solar related items from them with good luck.  I belueve my boyfriend has also looked into the place in Waterville for when we are ready to start renting items for the house build.  We have had really good luck with the ryobie one plus items.  We charge the batteries with our solar and are able to do tons of work with various tools as long as there is some sun.  We have also bought tons of cheap hand tools from local hunk shops and cleaned them up perfectly.  Eventually we will have to suck it up and rent/buy the big tools....Thanks!

I would let you use mine if I had one. Someday I should probably spend the money on one, they are only $79 bucks at Harbor Freight, but typically i wait until I absolutely need something for a job, then go out and buy it. I guess I have not got to that point yet, but then ledge on my farm is spotty. Oh it is here, but sporadic. In one spot it is above the soil, and twenty feet away you can did a hole 24 feet deep.