How do I toughen up Kayleigh's footpads?

Hi everyone - Sorry it has been so long since I have posted, but it has been a very "interesting" time over here (as in the Chinese curse of "May you live in interesting times")

I am trying to lose some weight by walking (because I just will NOT go to a gym!) and have discovered that Kayleigh (our two year old german shepherd) is the PERFECT walking partner. I just snap a walking harness on her, click on her leash, and away we go. She can walk forever at whatever pace I set. Yesterday, she and I went almost six miles and she was fine. We walk on the sidewalks and the grass and have been doing it for about a month and a half.

Today, I took Kayleigh over to the tennis courts at the Junior High so I could play fetch with her (these tennis courts are the nearest place where I can let her go "off leash" and she can run - her recall isn't the greatest when there are geese around to chase!). We run for about twenty minutes and she loves it. The problem is, her foot pads get abraded and start bleeding. It isn't a cut, they are scraped.

I don't want to stop taking her over there, because I never see such a look of joy on her face as when she is trying to catch the ball midair, but I need to get her foot pads toughened up so she doesn't hurt herself. I also want to start biking with her and her pads need to be tough for that. I read somewhere about some stuff I can put on her pads to speed the toughening process? Is there such a thing? Does it really work or is it snake oil? If it DOES work, where can I get some? Is there some other way to toughen up her pads?

I tried putting the "booties" on her, but she HATES it. . . . .won't move with them on. . . so THAT idea is out.

In the meantime, I have put the liquid bandage on Kayleigh's paws and it looks like I am on my own for walking until her feet heal up.

Any help you can give would be greatly appreciated!