I don't know what state you are in (state laws differ on hte details, but they all have this), but it sounds like he is trying to obtain title to the land through adverse possession. If you own the land or are willing to do the legwork for your landlady, find out exactly what the requirementrs are in your state, and do whatever is necessary to legally protect your land (which, sad to say, could include giving him permission to use your land (of course you can later revoke that permission, but at least it breaks the time that would count towards possession and the clock will restart).
He may feel that the amount of time needed has already occurred. However, for title to change hands, it does have to go to court. The land surveyor would not have that information as the courts would be the ones re-aligning the property lines.
I'm sure you realize that the folks suggesting you do anything that gives his cousin the Sheriff the legal right to come after you are just funning you. It is great to have fun on here but we do actually live in the real world. I'm not opposed to cleaning a gun on the front porch if the circumstances warrant, but there is a world of difference in cleaning a gun and threatening anyone with one, for example. Can you imagine how bad it could be to do anything that gives his cousin the legal right to start harrassing you?
Sounds like you have already had the property surveyed. I'd talk to the folks where you got the deed and see what they recommend. I'm sure they've seen it several times. It's probably your landlady's responsibility, but I don't know if she will do anything. As renters, you may be limited in what you can do. That may really make it messy or it may not be a problem. It would not surprise me that your landlady really does need to take it to court. I don't know the Florida laws, but you may not even be allowed to.
That sheriff may have actually given you the correct legal advice. You may need to get a lawyer. If he does actually harrass you or fail in doing his duties, the State Police have a unit that deals with police officers like that. That is a serious charge so I'd really think about it and make sure I'm right. I believe the FBI also has a unit that deals with corruption in local officials if the state doesn't handle it.
She knows we were just funning................ but if I still had the bull you could have borrowed him, he was kind to animals and me..... just didn't like anyone else. I doubt anyone would cut the fence to a snorting bull.............. but then that would have given you cause to go after him.
I know that area some.....I buy feed from Hillandale.... some of those people around those parts are strange.....