Otters are relatively predictable for trapping around a pond. Any secondary water source (such as a creek below the pond overflow or forage pond upstream) will typically have a crossover trail connecting them where the otter travel back and forth between the 2 bodies of water or they will swim through small channels of water connecting 2 larger bodies. They also quite often have toilets or slides where they come up on the bank routinely. Any of those spots make for relatively easy trapping with leghold or bodygrips. Recommend using drowning sets for otter or beaver in legholds. Beaver can be caught quite easily around their home area with a simple castor mound set using a leghold or conibear (where feasible and/or legal).
As for keeping them out, the only way I know of without "removal" is keeping a pond without fish.
