Homemade rc boat help?

ok so for my electronics final project im making an rc boat with chasing lights, i already have the circuit built however im wondering how to attach the propellers to the 9 volt dc motors, my teacher said you can submerge the motors but i dont know how would i securely waterproof it or should i just extend the propeller to reach into the water without the motor touching it. any ideas would be apreciated