How Can I Hide The Pond Filter

Build up around the filter with loose pieces of stone, put a flat piece on top.
Cover the vent with Spagnum moss. Keep damp.

we built a wooden cover/ box, that now has pots standing on and around it. the cover is easy to lift off. one side of it has plantings in the soil near to where it stand, but it depends what you are planning to do with the ground around it.