The "Accept All" opens the entire screen up for all targets to respond, and the "Reject All" blanks the entire screen to eliminate all targets. I use one or the other of those two functions when building a pattern from scratch. If I want to find just a few specific targets (and I know where they typically respond) I blank the entire screen, and then select the appropriate size of "frame size" editing tool and accept the areas that I want opened. If the hot rocks that you are talking about respond with for example 12 Fe/ 40 Co, if you reject that segment any good target that typically responds with the same 12/40 will be rejected as well as the hot rocks.
Page 9 in the manual explains how to accept or reject a target while detecting. If you have an undesirable target that is reading "12/38" (or whatever) and you want that eliminated, it is just a matter of using "identify button", to accept/reject that target, while the target response numbers are displayed. The manual explains it in greater detail........HH