I'm sorry to hear that your fellow Casanova has blood in his stools and urine after eating something on his walk last night.
I am concerned that this may have been rodent poison because he appears to be bleeding in multiple systems.
Is he having any trouble breathing? Any coughing?
Most rat poisons are anticoagulants, but some calcify tissues (cholecalciferol), some are neurotoxins due to brain swelling (bromethalin), and others are phosphide rodenticides which produce phosphine gas in the stomach and can lead to bloating and liver and kidney failure and seizures.
With long acting anticoagulant bleeding tendencies can last for a long time, the effects can last for 30+ days. We usually see effects from the toxin in 1 to 3 days, but sometimes it can take up to 5 or so days later.
Ideally if he ate this less than 3 hours ago we would induce vomiting, get rid of as much as the poison as possible, then use activated charcoal. But because he is showing symptoms that means the toxin is absorbed and out of his gastrointestinal system, it is far too late for that now.
He will need vitamin K-1 for 30+ days, and if the bleeding worsens he may need a blood transfusion.
He should see his veterinarian immediately to run a clotting profile and to get started on Vitamin K-1.
Other possible causes for multi-system bleeding are an inherited clotting defect, liver failure, tick borne diseases and autoimmune disease which attacks the platelets. Your veterinarian will likely want to look for those too depending upon his breed, other history (known tick exposure, Doberman breed etc.).
The important thing now is to have him seen on an emergency basis now before he bleeds too much.
Please let me know if you have any further questions.