Our pond has pine needles falling into it, so we have to pull them out
(annually, I see, after leaving it for two years and clogging the
pump). Our koi sweep the needles and everything else along the bottom
of the pond into the deep well (old septic tank), so we do not have to
clean the bottom of the pond itself. We only scoop the bottom of the
deep well. The pump itself is up on two sideways bricks and a cinder
block. That makes it about 12" off the bottom. That would be the
last haven for the fish if the pond got drained. We never have to
pull out the muck as it is stirred sufficiently that the pump easily
gets it at its 12" height.

We don't have a float switch to shut the pump off. We do do have a
toilet float valve that regulates the new water into the pond. It has
worked easily and well for the 13 years we have had the pond. It tops
the pond up when it has evaporated some. The only thing we have to
remember is to drain the pond down some from time to time so that we
are not always adding for evaporation but never draining.

Jim