On asphalt try to park so your cars are up wind so you can tie off to them for your rope bracing. legs can be held down with heavy objects....Coolers full of food and ice, cement blocks, weight lift weights etc etc. Tie rope to top of leg and down to the weight next to the bottom of the leg. Lots of times there are cracks in the asphalt if it is an older parking lot. We often could line up two of our legs with these cracks and nail down at least two legs this way. maybe find another crack for outside bracing. Nail stakes work better for the crack bracing. You need to come prepared for the situation you will be in. Its too late once you get there. Tom