There are different reasons for this.
It could be:
Urinary tract infection (UTI).
The easiest to deal with is the UTI. Once you clear it up the incontinence should stop.
The other causes can be more difficult and there are drugs on the market such as Proin, but they can have side effects.
There are natural remedies that work for some:
Soy milk at about 1/2 cup per day
A mixture of chinese herbs – www.pawhealer.com – has been recommended by a friend who had good results with their products. They should consult and mix your remedy.
Corn silk drops
Lighter weight in a dog with incontinence from reasons other than UTI is recommended probably because there is less pressure on the bladder.