My girlfriend and I are going to Louisianna for our one year ann.. How can I propose uniquely at a casino?

We will be going to a casino there with some of our family members. I want to surprise her in a way she never saw it coming. I had the idea of having the cashier slip it to her when she cashed out, but I am not sure I can be that trustworthy with something to that expense. Any ideas? We are going on Sept. 27th