How about putting something, like a playpen, around the pads so he can't wander off?
As a puppy, I kept ZoE in playpen with a potty pads & a bed. I didn't take her out of there to play until right after she'd pottied, so I knew I was good for a little while. Every time she went pee or poop on her pad, I praised her like crazy and gave her a yummy treat (usually a small piece of cooked chicken). She very quickly learned that to get the treat, she had to potty on the pad. After a couple of weeks, I opened one side of the pen, while keeping her confined to a single room in the house. If she pottied outside the pad area, I firmly said NO and put her on the pad and she got no treat. She soon learned that the only way she'd get a treat was if she pottied on her pad. Luckily, she was highly food driven and loved her treats!
She's now two years old, and will go potty on her pads (in the hallway) and come and tell me (by barking & kicking her legs back) that she went potty. She follows me as I go look to check, and then she quickly runs to the kitchen & sits waiting for her treat. It works for us, and she doesn't go potty anywhere else in my house, so I'm good with treating for potty, for life
