Hi I use this methood for Chelsey... I think i got the tip from someone here. Can rember who. Chester has not picked up on it yet and I don't think he will.
I bought a small bell on a look and put it on one of those hooks you can get from the hardware store that leave no marks on your wall when you remove it.
I measured were to put it so that chelsey and hit it with her paw.
What i did was everytime I let her out to go potty. I would let her stand near the door. I would ring the bell with her paw and give her a treat and then say out side.
Well I think I did this for two weeks. And then one day I had given her her food and closed her crate or at least I though I did. I went outside to the garage came back and was doing the dishes.. and hearing this ring, ding, ring. I could not figure out what it was. After ten min I went to investigate an I saw Chelsey at the back door hiting the bell with her paw... WOWO.
Well now she rings the bell more to go out and play not so much as potty.
Chester does not ring it at all. I tried with him too, but I guess he doesn't care
he just likes the treats. the bell was like $2 bucks. you can use anything. X-mass bells just put it on a loop and hang from the door or wall close to the door where they will go out.