the rebar is problely a waste of time. as long as you fasten the corners that is whats going to make or brake it. the pressure from the water is spread out so you just need overall connections you don't need to super renforce it. I mean look at a cheap swimming pool. Just use the lag screws and glue if you want and thats plenty. trying to drill for the rebar would be a very big pain in the rear. you have to worry more about rot then the thing exploding. keeping the wood off the ground would be the most effective thing. using brick or plastic wood on the ground will go a long ways to helping that. using a sheet of plywood on the insides to hold everything together would do more then the rebar and be easier. if you stagger the joints so the ends overlap and just screw them together that will be very strong. if you are worried get some 90 degree brackets to screw them together thats easier then rebar too.