I know it doesn't work for every dog, but my spayed female also developed this problem around age 1 1/2. She was put on PPA. When I decided to try something else more along holistic lines, I found after I took her off PPA the problem was much worse.
I randomly stumbled across a small breeder website who'd had success treating this problem by feeding grain free. Many years later I can say without a doubt this has worked well for us. She gets more than two (grain-containing) treats from the bank or pet store and she will leak soon after. But kept strictly to the grain-free diet she is perfect.
I currently feed Taste of the Wild and formerly fed Innova EVO. Both are great.