I have never been there, but visitors can't go there by themselves (and buy the entrance fee on site) whithout a "park pass"?
I was at Uluru recently and the only road into and out of the national park is blocked off by a gate. You need to scan your park pass to open the gates. They don't sell the passes on site, only online or at the hotel area next to the airport (and if you're picking up a car they can sell you the pass at the rental desk as well). Remember that these are very remote locations so access control is not that difficult :)