Make a wooden box from scrap lumber found at Home Depot. Drill a hole in each end. Place rat poison inside and set it in your crawl space. Only the rodents can get inside and eat the poison.
I've used a similar idea with empty peanut butter jars, any jar with a plastic lid will do. Drill a hole in the lid large enough for the rodent to enter/leave but not large enough for them to remove the bait. Drop in the bait block, screw on the lid and leave in an out of the way place. Check periodically and remove the small remnants of bait that could be dragged out where pets could get them, and replace with a full block.
We had an old rubbermaid container (with a lid) that had a hole in the bottom corner. It has been turned into the mouse poison center. Mice can get in and out, the lid comes off for easy filling of the poison in a low ceramic container, and the hole is small enough for only mice and not the cat or the dog to get into. I have placed it in the back of the garage on the floor and only we know that the container is not just for storage of "stuff" (like Christmas decorations).