It seems like people report mixed results when using diatomaceous earth to treat lice. I like to see studies evaluating differnent techniques and products. I found one study regarding DE (on mites not lice), it is titled:
"Effect of diatomaceous earth on parasite load, egg production, and egg...
Raccoons are great climbers and will be able to get over the top no problem.
Lots of people have had chicken wire on their coops and never have any problems with raccoons. But the fact is; raccoons can definitely get through chicken wire. Chicken wire is a deterrent, but not raccoon proof. If...