moving out in my opinion is extreme if he moves out then the neighbor wins not to mention he would have to leave his plants. and setting up a fence in a rental just seems like a big waste of money. call it a loss of a friend and some plants and move on, its not worth it escalating the problem...
what pepper seeds are you looking for? check my grow list and ill let you know if i still got seeds left
do you have any seeds and willing to trade they seem pretty intresting