I don't know about toughening up the pads on their foot's. But it seemed like every time I turned around, Harlee would rub the bottom of (or small part of) her paw raw. When she did, I cut up an old sock, put some Neosporin (cream) on it. Then tape the sock on.
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I started using 3M Nexcare absolute waterproof stretch tape to hold the sock on. I like that the tape stretches. They have that vet tape stuff that I also have on hand.
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In regards to boots. I bought Pawtectors.
I don't recommend using these boots for long walks on hot asphalt, and or concrete.
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Pops