Charlie P. (NY) said:
Garden trowels won't cut it. The Lesche is what I use where there are roots. In parks, as you note, where a knife shape freaks out the over-protective moms I use a tool I bought from Trans-Mississippi Electronics (P.O. 582312, Tulsa, OK 74158-2312 918-832-8064). Unfortunately, I believe the number is no longer in service.
This turns a deep plug and by cutting a flap it disappears when you put the dirt back. Park maintenance worker approved (last photo shows the hold filled and the divot replaced).