I just wanted to add that Bulldogs, while not the rocket scientists of the dog world, CAN learn, but are also known be very stubborn. So the key in any training is you need to be more consistent than he is, more stubborn than he. If the "pennies in a can" would freak him out too much, would a spray bottle of water do the trick? Some dogs, alas, think that's just the best thing ever, but it works as discipline for some.