Protecting wood fences from soil.

So I have places where I want to build raised beds right next to wooden fences.
Some of the fences are treated wood,  some are cedar,  some are pallet wood.
To prevent or retard rot,  I want to use a barrier.

I think plastic sheeting   by itself is doomed to be wrecked by sun exposure or wear.
I was thinking if I use it all it will be in conjunction with a protective barrier.
An untreated  wood barrier could be almost free but is itself doomed to rot away.
I can get cement board for about 33.00 cents a square foot.
It's pretty durable, survives exposure to water readily,  but it might leach nasties.
Tiles I can get for 50 cents a square foot.
I'm pretty confident they won't really  leach under these conditions, plus they are totally waterproof.
Petrified Hessian is burlap soaked in cement.
I can get burlap sack for free,  but I have no idea what the per square foot cost for the cement would be.
With any of these I think I'll install furring, to create an air gap.

What else could I use?

Recycled steel or alum roofing?

I like the idea of tile from a longevity perspective, but what will hold it together?

Cementing the burlap should be pretty cheap on a square foot basis..

If you stack soil against the fence, it may be pushed over by the soil.

William, if you made your raised beds out of construction concrete blocks, the first layer sunken halfway into the ground, the second layer alternated over the crack between blocks, allows for airflow near the wood, let's you redesign the shape of the bed if you change your mind, you can plant in the holes of the concrete block, and they will last forever, pay for them once and no replacement necessary, won't attract termites, if they are in your area.  I got a ton of termites after just one year of wooden raised beds.

Or if you still want wooden raised beds, a layer of concrete block between the raised bed and the fence keeps the wood from moving or bulging, and allows for air flow through the concrete when it gets wet, which allows the wood to stay dry.  The decorative concrete blocks are the thinnest, the kind they used to make patio walls out of in the 1950s.  The other construction  blocks work fine as well.

A plastic barrier would also hold moisture next to wood, causing wood rot.  

My fences are pretty stout,  so I'm not worried about them being pushed over by the soil.
The tile will be held in place with metal or wood stakes, and eventually by the weight of the soil against them.
The tile is much stiffer than the other options,  plus waterproof on its own.

Aluminum or steel panels would be great,  but if I could've afforded those,  I would have built the fence with them in the first place.

I think I'll save the petrified Hessian for the north side of my greenhouse where I won't have much if any soil against it.
I really want to try it somewhere 🤓!

I can't reliably get used concerete block, and the price for new is very high per square foot.
I  agree,  plastic against the wood  could gather condensation and precipitation.
It would be able to dry to to the outside,  but why risk it?
That's why I'm also going to space the barrier off the fence with furring.

Pulled the trigger on buying tiles.
12 tiles,  1'x3' for $15.00, covers 36 feet of fence line.
The missus is gonna double check the available hours of sunlight against this fence before I commit to building this bed.

Here is a photo of the bed,  almost filled.
My daughter is reclining in it, as she is apt to do.