If it's anything like the rental property we own that have a pool/clubhouse, the association has forms in the office that the tenant has to sign in order to use the pool. Check with your HOA on whether they have one or not. If they do, you can always take it to your lawyer if the agreement doesn't contain enough in it to make you feel more comfortable. If they don't have one, you may suggest at their next meeting that they have one drawn up. They don't have to reinvent the wheel, other POAs have them.
Second, check with your insurance policy regading liablity coverage and their requirements from you.