You're not giving us the whole situation. Does he pee in his create every day, or just days that you leave him in there for more than 3-4 hours? When you're home, does he want out more often than he should need to go? After going outside and peeing, does he come in and have accidents shortly after? Has he been doing this since he was a puppy or is it a newer behavior?
I had a Doberman who had a similar problem. He had it since he was born(the breeder just never noticed). He'd pee in his crate every single day. I'd take him outside, he'd pee, we'd go back in and he'd pee right away. As he got older we found out he had a bladder infection(after my vet reluctantly deciding to take a urine sample, no longer at that vet because of her) but after that was taken care of he was still having accidents. At 8 months he could not hold it all day in his pen. He was finally diagnosed with Pelvic Bladder, his bladder was up between his pelvic bones so he couldn't hold as much urine in his bladder as a normal dog.
Your dog could have a bladder infection, or he could have
elvic Bladder, or it could be Seperation anxiety like the other posters said. That depends on what your answers to my questions are.
Shiva