I used to do that but when I got a bunch of drunk birds I had to cover the containers. You need to have the beer deep enough that they drown in it, not thin so they get buzzed and come back later. Use a small net to scoop out the dead slugs and leave the beer for more. The only alternative is a commercial snail poison which is not good for kids or pets. Sluggo works around these but it is not as good as those that have an attractant in them.

I think you need to start brewing your own at home!