Tips for potty training a very fluffy puppy in summer?

We added a Keeshond puppy to our family about 10 days ago. He is about 9 weeks old now. He's very young, so I don't expect potty perfection yet, but he was doing pretty good about not going in the house. He has little signals that let me know when he's about to go, and sometimes he'll even whine at the front door, which is great. However, we've had some setbacks in the past few days. The weather here has been insane - 90+ temps and ridiculous humidity - and he's a cold-weather dog with a double coat. He HATES being outside in this heat. Now, when I see his little signals or when he cries, I take him outside and he immediately drags me back to the front door and whines to go inside the house. The weather bothers him too much for him to even stay in the yard long enough to pee. The problem with this is, once I let him back into the house he immediately goes on the floor. We went from having 0-1 accidents per day to 4-6 accidents per day! It is getting frustrating because we were doing so well and I can see all our progress disappearing. A friend said I should chain him in the yard and just wait until he goes, but I hate to make him suffer like that - it is truly awful watching this poor pup try to cope with the heat. I put a little kiddie pool in the yard to keep him cool, but even the relief of the water hasn't encouraged him to pee in the yard - he just gets out of the pool when he's cooled off and runs to the front door again. I'm almost considering getting him shaved! Has anyone else had a similar experience? How did you handle it? Thanks!