Other causes of bloody mucoid stool besides GI parasites include ingestion of sharp GI foreign bodies, toxins or chemicals, Parvovirus, or other viral or bacterial infections, pancreatitis
You could try giving your dog
Pepcid (famotidine), and Sucralfate, if you have access to these medications to treat the symptoms. Pepcid is available over the counter in most countries. The dose is 20 mg once or twice per day as listed on the bottle.