Shaft through metal under water

I know this is more machenical, but im building an under water turbine. Has any one does this. I need an water proof casing and currently the problem is having the shaft to go in to the metal casing without letting water and sand in, iv googled it, cant seem to get what i want. does any one have any good resources on how to do this. Thanx

oh and i dont want it to complicate on myself either.

Try googling "stuffing box" which is what boats use.