It's your land, so you have EVERY right to it. Bring it to the police again, with whatever evidence (photos of chain on your land; the name of the buyer and the realtor, also the worker who were harassed, so they all could be contacted if necessary) you have. If the first officer you speak with isn't interested in helping you, go to his supervisor.  Vandalizing, trespassing, putting up a structure on your land--these are crimes, and should be treated as such.You might also get an attorney as well--you might want to file for a protective order, as well as have a letter sent to your uncle and his son that if they interfere with a sale again, you will sue THEM for the full sale price of the land.Rights and the law are on your side--you just need to hang tough.One last though--double check any deeds and surveys to make sure you can prove the extent of your land.