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*I understand nothing is bullet proof, but having something is better than nothing.
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Not neccessarily; a good injury lawyer would use that paper to show that you were acting in a professional capacity and that you knew the activity to be dangerous. Courts routinely throw out "boiler plate" forms, especially when the text requires the plaintiff to give up rights granted to him under law. To put it plainly, if the law says the injured party is due compensation, due to negligence, for instance, then his scrawl on your form doesn't remove that right from him. It's where the use of the term 'boiler plate' enters the legal language. The boiler makers would stamp warnings on the brass plate on the boiler and later hold that up in court as sufficient protection against liability. The courts ruled notification as insufficient protection against negligence, or something like that.
Now I don't know Ohio and I'm not a lawyer, but here in California the only way to do what you are proposing, and not risk your house, your car, and every cent you'll ever make, is to have the local community college underwrite the venture. See, the lawyers are going to go after the one with the deepest pocket. You want the deepest pocket not to be you. With the local college involved, or trade school, or ???, then they hold the million dollar policy, their name is on the class form, and you are just a temporary employee of the school. There are not a few shops in my area where that is the only way to get on to the property.
It's also general practice in California to have at least a million dollar general liability policy on the property if there are any unusual hazards, such as machine tools, on the property and those areas are open or accessible to the public. This has to be done in concert with the community college thing. The school takes on the specific liability for the class activities and the general liability policy takes on the incidentals like falling in a hole or power wires falling on someones head.
Now maybe in your state there is another way, I kind of doubt it, that is why you need to speak with your lawyer.
What the local rock hounds did is to pool all their equipment and form a club. They got the club sponsored by the local city parks and recreation. That way when someone gets a rock chip in their eye or sticks his finger in the rock saw blade it's the city's headache.
Edit: I'm unable to find a reference to my origin of the legal use of the term 'boiler plate' so don't quote me on that one.