Tree line fencing questions.

I have spent the last two days cleaning up my overgrown fence lines. The fence line was fenced at one time with high tensile for horses. There are a few t-post, but most of it was done by going tree to tree. I want to fence off several acres for sheep and a guard llama, with 5 foot goat wire. A lot of the trees in the fence line have grown to massive size. If I go around each and every tree the fence is going to be all wonky, if I bring my fence line in, I'll be giving away lot of land away. I was thinking of maybe setting a post in on each side of the trees that are in the way. Is the a viable solution? I know this would for a lot more posts, but at least the fence rows would be straight. I have never tried or heard of anyone setting a post in direct contact to a tree before.

My next question is about fencing across a slope. Part of my fence line is on a slope so steep, I could almost step over a 5 foot fence. Granted in would be a long fall plus lots rolling before I ever stopped again. Is this something to be worried about?

Any advise will be greatly appreciated.

Personally I advise you move the fenceline away from the trees. You can put up clear markers for your property line based on the old line, if you're concerned people will think the fenceline represents the property line. I think trees along fencelines are a benefit to birds and other wildlife, and you'll be able to better maintain the new fenceline because it will be free of trees. You may have to use extra-tall posts and an extra row of wire to adequately fence the steep portion, if you can't reroute the fence to a less steep location.