You could foot the bill for a $4 bag of feed, chickens require special feed for what I'm about to tell you, then pour it in a pile on his property at the edge of where they hand around. Buy the right feed and they'll begin laying eggs. Chickens that roam start laying eggs whereever and before long he'll have a dozen spots filled up with rotten chicken eggs. Or, make good of the situation and collect yourself some fresh eggs. Either way, short of killing them, you aren't going to get rid of them because they hang around. Out of seven we had we still have one that roams the yard thinking it's a cat, it comes when you call it and likes to be carried around a petted.