This has never been a problem for me, save a handful of scenarios when a person was in clear breech of the rules. My personal policy is to offer the surrender rule early and often. Anytime I'm a bunker away or as close as 25' (the field's official zone is 15') I make it clear my intention is to come get them and their only alternative is to leave the game.
I guess the key is that I make any potential surrendering/bunkering victim aware of the situation, and by removing the element of surprise it really helps to clear up any confusion. Of course this may not work as well with other people who take a sneakier, stealthier approach to the game, but it fits into my hyper-agressive, always advancing play style well.