A check valve would solve the problem, however... You will be restricting the flow through the hose, by as much as 30%, so your 500gph pump now becomes a 350gph.
I have never been a big fan of the automatic pumps and switches. I have mine wired to a breaker in the panel without a float, and routinely hit the switch whenever I board the boat, or during extended motoring (I like a slow drip at the propshaft stuffing box, keeps things cool). And you may become complacent, thinking that your automatic will always take care of things "down there". Its always a good idea to lift the boards and take a peek to make sure everything is fine. Plus, you won''t have to worry about a drained battery from a constantly running pump.