I have a property boundry separated by a wooden fence that is in need of replacement. This fence completely encloses my property. My neighbors yard isn't enclosed, in fact this is his only fence on his property so I feel I have more 'right' to it (I think some states have that view). He hasn't maintained the fence at all and thanks to that it is now rotted. I want to replace it, he doesn't. He thinks it is okay even though boards are falling off. He did offer to throw in $350 even though it will be $1000 for materials alone and I will be doing all the labor (I did another side of my yard already so no big deal). I need the sturdy fence to contain a dog.
Can I go ahead and replace it without approval and is he REQUIRED to pay for it? If he pays for some, but I pay more and do the labor, can I design it anyway I want (put the fence up so the cross beams face his side)? If he doesn't want to pay for it and I put it up anyway (which I will), does he have any right to it or have to maintain it? Should I let him know when I will be doing it and that I may be 'on his property' during the process (trespassing issues if this gets ugly)?

