We catch a lot of our cray fish for bait and do quite well over the summer. I know what you guys are saying about leaving traps out over night on lakes. Had 2 stolen last year. That had nothing to do with kids taking them as much as we set traps in an area that someone claimed as their own. After we moved them to another area we have had no problems. Also if you have problems with people takeing them, take them out at last light and get up at first light before most people are out of bed. We have yeilded couple hundrend dozen in a weekend using only 3 traps. Those kind of numbers come of the sides of shallow rock bars setting traps in 6-9ft of water. Using traps I have found though have yeild crayfish on the smaller side. If you never tried, and have a lake that has a healthy crayfish population, find a sandy shoreline and take a flashlight at night. I have spent many hours walking the shore catching them little buggers. Great fun for kids and you can find some bigger ones. Agreed that you dont need to find a rocky shore, but defanalty cant be a mucky bottom.
As for bait any FRESH fish guts will work. The key is fresh or fresh frozen. Dont leave the guts sit in your traps for more than one day. I have also noted that if you use a "bait box" within your traps to hold your guts, they dont seem to do as well as just leting the guts free float within your traps.
Im not sure on the legality of using a float that stays under the water. I wouldnt recommend using that. What happens if you wreck someones motor, or worse if someone would get hurt because they couldnt see a rope under the water. Just my two cents.
Love eating them little buggers. Share on how you like them cooked. Me personally I just like them boiled with salt and fresh dill.