I use a belly band on my boy. Even though it hasn't aided in the potty training process, it has given me peace of mind when im at home. I dont feel like i have to crawl behind him every second of the day. Plus I got so sick of cleaning the carpets!!!!! I just put a sanitary pad in it and change those out.
Here is the site that I ordered from. Next time I order from here I will probably get a size which is a few inches bigger then his belly since the pads make it a snug fit.
http://www.dog-breeds.net/dog_diaper_belly_band.htm