I'd put some game cameras out there where you keep your tractor!
X2, plus if there has been NO issues to date and after u file on him for his act and then stuff starts happening to ur equipment, its no coincidence and wouldnt be hard to prove, especially if the trail cam caught him red handed. U say there is another case in ur area of a similar act. Then by bringing urs to light, it may show the judge and jury (if it goes to a jury) that shooting a dog/s is happening and the dog hunters will not continue to let it happen with no repercutions to the shooter. Yes, it could go his way with a slap on the wrist but it could be the "straw that broke the camels back" so to speak and the judge throws the book at him or the other shooter in the other case. Even though he dont have much so to speak, that shouldnt mean he gets a free pass. He should be held accountable for his actions, just as we ALL are on any violation of the law once we get caught. It would suck to take nearly everything he owns n possibly him going to jail, but that may be exactly what he needs to wake him up n open his eyes.
Like u said, growing up, he made claims that he n his family shoot dogs that wonder onto their land. U mite have taken that as just talkin chit growing up, but now uv seen it first hand. Why take a chance again with him or possibly any other fellow hunter hav to go through the same mess or worse, u or the nxt hunter loose the dog completely bc u sat by on the sidelines.
No matter what we as a group may say/recomend u to do, it is u that will make the final discission. Ur dogs didnt deserve to get shot, so by not pressing issue with the law, ur dogs took a bullet for nothing and its not fair or right for them to be punished for his crimes.