I think the routine is most important and watching for their signs. We got Mocha the bells and he thought they were a great chew toy. Then DH saw the Gotta Go button and we got that. Whether routine or we saw his signs, we would hit the button we went out the door. At first, he didn't have the paw to eye coordination to actually hit it. But he does now. However, he does hit the button just to go outside to play. But I think that would happen with any signal you teach.
Also, cleaning up any accidents with Nature's Miracle or similar cleaner.
One of our friends loves that button and asked how we trained Mocha to hit it. DH told him we just put the instructions on the floor next to the button and Mocha read them!
Amazon.com : Gotta Go Button : Pet Door Doorbells : Pet Supplies