What I always did as on OF was play normal depth and backpedal on the pitch if the guy has pop. I figured, standing at 265' I can track down most deep balls from average players. The power hitters I would at least have an great jump on a bomb but still only be at about 275' if they hit it in front of me.
Also, I noticed on fenceless fields less skilled or experienced guys see you playing "short" and overswing trying to beat you and you get a lot of pop ups.
Of course, no amount of backpedaling from 265' is gonna let you catch a ball hit 365'. But if you're playing deep enough to catch something hit 365' you're probably playing too deep and every ball in front of you is a double.