I rotate between Tomcat All Weather Bait Chunx and Tomcat Mouse and Rat Bromethalin Bait Chunx. Amazon, Tractor Supply, and several places carry them.

One is an anti-coagulant, and the other is a neurotoxin, so you don't have as much trouble with the rodents developing resistance.

They both have a hole running the length of the chunk. I always put a nail through the hole, and fasten the chunk to something. Otherwise, rats, chipmunks, etc. will just carry the chunk off and store it without eating it.

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Boots were made for walking
Winds were blowing change
Boys fall in the jungle
As I Came of Age