Apply pool putty around any cracks on the sides of the pond skimmer. Skimmers are made of plastic and can crack when the temperature reaches freezing. This causes leaks. Pool putty or epoxy putty compounds will creaked water tight seals so water will no longer leak out of the skimmer.
Use a mixture of plastic patch if the pool skimmer becomes separated from the pump line wall. Ground movement can break this seal. Apply the plaster patch to the outside of the skimmer unit and press it to the pump wall. This may have to be done annually depending on the ground in your area.
Turn the pump off if the skimmer should clog. This is the most common pond skimmer problem. Insert a hose into the pump. The goal is to force water back through the pump and pond skimmer to unclog the skimmer. Turn the water on full to force the clogged material out of the skimmer. Check to make sure that the pump is not clogged as many times this is the problem instead of a clogged skimmer.
Replace the skimmer flap if it is worn away or cracked. Many times the rod at the bottom of the flap will wear away. This causes the flap to not work and keep debris out of the skimmer. Replace the rod at the bottom of the flap or replace the entire flap.