Jackson was almost 7 months old when he was neutered. He was around 6 1/2 months old when he hiked his leg on my dads furniture in his screened in porch (which is carpeted). It was the first time he had ever lifted his leg and I went uh-oh! and scheduled his neuter a few weeks later! lol. He has not marked ever any other time indoors since. He will lift his leg on walks, etc outdoors but it's not obsessive. Basically, I don't think your doomed for life. If he's only done it twice, just keep a close watch on him so he doesn't/can't do it anymore and then get him neutered. I agree with LadyMom, I don't like belly bands because it just covers up the problem and doesn't address it. I wouldn't wanna have to depend on them for the rest of my dogs life if there were other options!
Good luck! Btw, I love your new avatar pic!