Hi Travis,
I'm in SE Michigan as well, and have a huge slug problem. Made an asparagus bed last year and mulched with about 6" of woodchips. Even a fast growing perennial like asparagus could not keep up with the slugs mowing it down every night. The last 2 weeks of dry weather coupled with D.E. applications have helped that bed substantially.
But, another option that has worked in our garden is red clover. It seems that the slugs love to eat the clover and prefer it over other plants. I planted clover in our garden pathways last year, and we didn't have anywhere near the amount of slug damage that we have had in the past. Of course it would take a month or two to get the clover established, but once established they do seem to be attracted to it.
Of course, depending on your garden layout, the clover could become a problem by spreading into areas where you don't want it, but so far we have not had that issue. We simply chop and drop the clover before it goes to seed, while always leaving some behind for the slugs to eat.
It feels weird to be almost encouraging the slugs by giving them something to eat, but the ecosystem is so out of whack (ie a billion slugs compared to the minimal number of predators), that it seems to be worth it. It also seems that the clover provides more habitat for the predators to congregate and we have seen an increase in snake/toad/frog populations in the few years that we've had our property.
