Protecting our family farm legally

Post "no trespassing signs" on every few sections of fence post. That ought to establish that people are not welcome, and if they get hurt, it's their problem for not following the clearly posted expectations. However, in some cases, horses are considered an "attractive nuisance", as in, they attract people to them even though they can be dangerous to those same idiot people :p

Not sure how that would pan out, I'd ask local law enforcement, to be sure

I own a quarter section of prime deer hunting land which makes it quite attractive to hunters. At one time we had to post the land, very difficult because of areas of heavy bush or water. Our ministry of natural resources changed the laws and put the onus on the ones who don't own the land to find the boundaries. There are two enforcements we can call, either the police or the ministry officers. What I learned last year was that calling the police meant that with the charge the person/people may be denied access in to Canada. We caught an American who'd set up camp on my land and made threats when told to leave. The police were called, didn't find him that day but he was caught when crossing back into the US. People don't realize that even a minor charge might screw up foreign travel plans.

Alabama only allows deadly force in defense of life and limb, see Code of Alabama - Title 13A: Criminal Code - Section 13A-3-23 - Use of force in defense of a person - Legal Research

Humm have to do a search, see where you can shoot horse thieves.