When we moved we had to retrain our dogs completely. We watched them all the time, put up gates to confine them in the area/room we were in (we still do this), and took them out every 2 hours on the dot and made sure they pottied. When they did go we would praise and treat like crazy. It helps to find a treat that is really worth getting.. they catch on quick that way. We used cheese. It was different for us though because my dogs have been confined while we're away or asleep from day one. I'm not sure how you would go about properly retraining a dog without confining it. My suggestion would be a belly band while you're away so in case he does have accidents, it doesn't stain your carpet.
Any kind of transition is hard for a dog. Even my dogs, who I would consider fully potty trained, are having trouble with my roommates new dog. They now also sometimes pee in house so we're adjusting and dealing with that currently.
We have a portable steam cleaner that is perfect for cleaning up little stains as soon as they happen. An upright one would probably work better but would be more of a hassle considering you'd have to move all of your furniture and let it dry overnight before stepping on it. We have one of those also but only use it every couple of months. The portable one is out every day and used quite frequently. Aside from dogs it's great for any kind of spill. The one we have is
Walmart.com: Bissell Little Green ProHeat TurboBrush Pet: Appliances Just soak up the pee, saturate the stain with Nature's Miracle and let dry for 24-48 hours. Then go over the stain with the steam cleaner. I don't like the pet solutions.. they don't seem to work as well. We use Woolite Deep OxyClean or just plain OxyClean mixed with water and it does a great job of getting stains out.
Good luck! Let me know if you have any more questions. :animal-p