My rubs usually contain some salt. However, I usually sprinkle some rub on the meat and rub it in. What stays on during this rub stays. What falls off goes.
Some people just sprinkle their rub on wet meat and hope it flavors the meat. Some lump it on, play patty cake with it and pack down the rub so you have a layer of rub. I find most of the rub falls off, or melts off during cooking.
I've used mustard to hold some rubs on. I've got a bottle of chipotle mustard sitting on the shelf. I'm thinking of trying that one of these days.