My dog’s p***s has been bleeding, help?

My mom called me while I was at school today and told me that Ringo’s (my half rottweiler half pit bull) p***s was bleeding profusely. I hurried home to see what was wrong and examined him but he had no external cuts that I could see. The bleeding stopped and he seems fine now. No weakness or wooziness or other symptoms that I could see. I watched him for a while after that and he has no trouble peeing and no pain or blood in his pee.

We live out in the country of west Texas, so there’s a lot of thorny brush around. He’s a big dog and likes to chase rabbits so I’m thinking he jumped over a thorn bush and scraped his p***s or something.

Is it a good idea to put him back on his chain to prevent him from running around and re-opening whatever he caused so it can heal? Or should I take him to the vet tomorrow just in case? Could this be something really serious?