i know this may sound strange, but our vet recomended using black licorice, something about it helps control the hormones in their bodies. we simply gave it to him everytime he went outside.
Also if he has an accident, after you use warm water use white vinager, it makes the smell invisable to them. Other cleaning products simply challenge them to cover it up again
__________________ Xander  Addie  Willow  and Rogue |