How old is your dog? I'm a clean freak and it gets wet in my fields often. I taught my dog to lay down on a rug when he enters the house. There are rugs in front of all doors. He waits till I wipe his feet before he can leave.
When he was a pup, of course he thought it was a game and wanted to grab the towel. I knew he loved small soft toys, but he would destroy them quick, so they were off the menu. When he went into a sit and then down position, I gave him a soft chew toy. He'd see the toy so he was quick to follow instructions. After I gave him the toy, he'd be so happy, he coud care less that I was wiping his feet off. When I was done, I made him give me back the chew toy. I'd put it back in the drawer and he was released. I have to admit he would look sad when I took his soft toy away, so I usually gave him a couple Zuke mini treats.
After awhile , I didn't give him the soft toy, he simply knew to lay on the rug and wait to have his feet wiped. Sometimes he might be a little fired up and will try and grab the towel, but a firm "leave it" should work after your dog understands these are the rules.
So, get a soft chew. If it has a squeaker, thats even better. I bet he lets you wipe his feet and that towel will be a heck of a lot less interesting. After awile you won't need it. Remember even when it's not wet, enforce him laying on the rug or near door everytime he enters the house. I might know it's dry outside, but he doesn't. I'll reach down and touch a paw and then just say okay. My dog is 13 months old now. Good luck.