I dig my plug as a flap either C shaped or squared and flip it like a book cover on the ground. Typically that in itself will be 3 or more inches..then set scan the plug and hole, if the item is still in the hole I put my ProPointer in the hle and scan to see if it has depth, if not I put my drop cloth right at the edge of the hole and scoop out the dirt onto the cloth then scan again with the PP. When I have located the item i can grab the corners of the cloth and replace the dirt without making a mess and flip the sod flap back into the hole. Typically i will pound it down with my hands then give it one last press when I stand up. More often then not the hole is clean and clear and cannot tell I was digging. Thats how I like it.
On a side note I was at an old school earlier in the week and spoke witht he custodian and asked if he was ok with me huntign there and his biggest complaint was some others who have gone through leaving holes and obvious signs of their digging. He was concerned for peipel tripping in the holes etc. He came out and saw how iw as recovering my targets and then told me about 3 other places i could go since I was being respectful and returning the ground to such good condition and removing the hazards as I dug them. (found lots of glass and glass bottle tops witht he metal caps still screwed on them.)
Good luck and Happy Hunting!