We went to Ashmire Fishery Cambs last year, place was fenced, main gate looked very low on arrival like 2.6 - 3ft max - I started in peg one by the gate, 2nd night my dog went out to something that scuttled past the back of my bivvy and vanished. Hour later we've got an otter swimming around chasing the swans all night - poor things were so stressed.
Before leaving 2 of us went to see the owner, I told him the gate was too low and that was the entry route but he wouldn't have it, it must be a badger hole in the out of bounds he says, very little we can do about badgers. Guy had his head in the sand - crazy man will lose them all over time, was nowhere near bothered enough.
My last syndicate was fenced but the initial/emergency fence was chicken wire, over time the wire weakened in the wet areas and a small hole was forced and one got in. Killed my target fish (two tone), nothing was said and I wasted 5 years chasing a ghost! Owner there is well on it, fencing is all improved and has additional electric wires yet he reliably informs that they (otters) still check for weaknesses every night (trail cam) - it never stops - any storm damage and they will be straight back in!