As a rule when there are pet stains on the plywood, your best bet is to replace it as it is almost impossible to get the odor out of boards. However, i do know of a very good cleaner for pet stain and odor on your carpet or fabrics, you could spray this on and see how deep it is. Usually though everytime a dog smells this odor spot, he or other dogs are sure to find it, so think twice about covering it up, sometimes a little extra expense is worth alot of headache latter down the road if the odor comes back. The cleaner is: CAPTURE pet stain and odor neutralizer. This can be found at Lowe's.