no expert ,but i would think you ll tell the differance by smell of hole,and size of throw back,along with localy placed shit pits ,or food out side of hole if foxes are using it.
lol that statement reminded me of some trips we had up to pensycynor wildlife park to relieve them of some large trout that looked better on the tables of hungry miners kids.
has penyscynor still got the tobbogan run
happy nights spent there
penyscynor is now a persimmon homes housing site lol