How often does the system regenerate? Does it actually use the brine? Mine has a little filter on the line that ***** the brine, where the line goes into the head.
Is there just one broken tooth? Years ago we had an Allis Chalmers B tractor, the ring gear was bad in two spots where the engine would stop. I welded up the teeth and ground them to shape with a 4" angle grinder. Worked fine,
I have used a hammer and punch, but it will deform the nut a little. Otherwise, I have seen pics where someone will make a tool. Either a proper sized socket ground out to fit, or a piece of thick steel cut to fit. Those nuts are extremely tight.
I have drilled a couple that I could not get out. Used a bit about the size of the lug, probably like a 7/16 or so. A sharp bit goes pretty fast, the lug and nut are not hardened.
The only thought I have is to check on local building codes. Where I live, a permit is needed, and there is a lot of regulations regarding fences. You should also have a locate done for underground wiring.
Since you may have termites in your area, after framing but before you finish off the inside, you could spray some Boracare on all the studs up 12" or so.
I've been told the reason for tar paper is to keep the shingles from sticking to the roof sheathing. Without the paper, it would be difficult to remove the shingles at the next re-roof.
I had a roofer tell me that on some roofs he has shingles, the shingles stick so good to the ice and water...