There was an unfourtunate storyof a yid whose non jewish wife was only prepared to allow a jewish burial if she would eventually be interred adjacent to him.
If i remember right the question was brought to r’ osher westheim, who eventually referred it to r’ yisroel yaakov fisher zatza”l, who allowed him to be buried at the side of the beis hakevarois with her next to him. I don’t know if they required a fence.