On some boats prop walk ceases to be a factor once you're at a maneuvering speed in reverse... if this is not the case then shifting to neutral strategically should help.
Other boats, however will slowly turn in a particular direction regardless of your efforts to "steer".. these are the most difficult to deal with in close quarters. In this case learning the boat and trying to set yourself up for the easiest move will help. (ie choosing to back in to make leaving easier, or vice-versa), or as Adam has pointed out leaving one way in certain conditions and another way if tide/wind is reversed.
Poor reverse performance has always been one of the 'deal breakers' for us in our boat selections.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)