Is he peeing when you leave, or is it when you come back? If its when you come back, what do you do to greet him? Do you aid in his excitement ... even if you don't mean to? What is actually happening when he pees? Are you bending over him? Are you using a very high pitched or low voice? Have you scolded him when he does this?
If its happening upon your arrival, or someone elses, your best bet would be to ignor him for the first few minutes when you return. Don't make coming or going (or anyone else coming, or eating etc.) an exciting event or a big deal. Tone it down, if you can. Once you've ignored him for a few minutes, get down on his level and give him some attention when he's calm. Don't pet him over the head or back - scratch him on the chest, use a regular voice when you take to him, give him a treat or two for being calm. You want him to eventually realize that coming and going are no big deal and nothing to get excited over. You want him to also realize that he doesn't get attention when he's excited, but he does get attention and treats when he's calmed down.
I would suggest to crate him while you are eating, perhaps giving him a kong stuffed with something yummy. You can eventually wean him out of that, but I'd work on reducing the excitement levels in the other instances first.
On a side, has he been checked for a bladder infection?