Bell training is wonderful. Hang a bell at nose level beside the door and every time you go outside potty, ring the bell. Once Tugboat associates the bell with potty, have him nose the bell or paw it to make it ring. I prefer nosing even though it doesn't make as much noise. Tugboat will catch on in no time. Some of the smarter/mischievous pups abuse the bell just to get outside to bark and whatnot.