Electricity

I have made a small pond for a turtle. I'm wondering if anyone has a
technique for connecting electricity in the outdoors. I'm concerned
about moisture getting into the connection as I had a problem with an
aquarium filter splattering on a connection and causing a tickling
sensation in my hands when I went in to unplug it.

For now my concern is adding a heater to the pond to get it warm enough
for the winter/nights. I was thinking of just the end of the electric
cord in plastic and taping it sealed. The pond is nothing too elaborate,
just a tub inserted into the ground. I have a filter that I'm working on
connecting to a power socket too.