If you are at the point of replacing your mats, you might want to look into stall skins. Instead of having seams, they are designed to fit the entire stall floor and be waterproof. I haven't personally used them, but it seems they would work better over something like concrete that doesn't drain, as it would keep the urine on top where it could be soaked up. I haven't compared the price of stall skins vs rubber mats, but I would imagine it would be similar. Just a thought.
"Keep a leg on each side and your mind in the middle"