Usually any rodenticide that gets wet can lose it toxicity. That's why most that are made for outdoors are wax based. You should always use outdoor rodent baits in a sealed device called a "bait station" such as the EZ Klean
. This helps prevent animals and also rain from getting to the bait. Also, you should never place exposed rodent bait outdoors under any circumstances unless it is underground or in an animal burrow or tunnel.