Is there a reason you are using a pee pad instead of making him go outdoors?
If he's 8 weeks or so he needs to be going outside every hour or so, and immediately after eating, napping, play sessions, etc. At that age they have very little control over their bladder. You need to be watching him 100% of the time, and put him in a crate or xpen when you're unable to keep an eye on him.
Pee pads just teach him to go indoors. If you cannot take him out as often as he needs, confine him to a safe, uncarpeted area and just use newspapers in a part of it. Clean with a water/white vinegar mixture when you change the papers. It is not just a matter of training, it is also a matter of maturing, bladder capacity and acquiring voluntary control over an involuntary natural body function. If you crate the dog for long periods in the day (longer than he can hold it) he will learn to pee in his crate and this habit is hard to break..... At night, you will probably have to take him out at least once, until 10-12 wks of age.
I didn't use the wee wee pads personally when housebreaking Selkie, I used a grass turf pad. But I only used this when I was away from the house for extended hours and kept it in her x-pen with her. To get her to use it, I took an old towel and soaked up some of her urine when she went outside to potty and placed the towel under the turf pad so that it would attract her to her own scent and teach her this is where to potty(which is what the housebreak sprays are supposed to do with chemicals).
But again I never left it in the house for her to use whenever. We always took regular potty breaks outside. Always stay vigilant, take him out after he stops playing, when he wakes up, when he changes activities, you can make a startled noise if you catch him in the act and scoop him up and take him out. Good luck!
Fergus is just 6 months old and we were pretty accident free in the house by oh 12 say 14 weeks and all I did was simple..... we play -- go outside -- we wake up -- go outside -- we eat -- we go outside -- wake up from our nap --- we go outside. I think you get the idea. They are smart and want to make you happy just praise them when they do their business outside and say to yourself ....... Self you should have been taking him outside not watching that Lifetime Movie =-) ... when they have an accident.