If the dog can't tolerate ivermectin, there's always the old standy: mitaban dip. We found a starving, mange infested, staph infected pup and it took 4 years of slowly decreasing dipping before his immune system could fight off the mites. Well worth the effort though. :-)
Having worked as a tech for a vet dermatologist we saw a lot of demodex. It is a hard condition to treat but you must get a vet who knows what they are doing. Oral Ivernectin is the best and most effective way to treat. your vet needs to do skin scraping in between the toes and look under the microscope to keep track of the number of mites and whether they are alive or dead. They'll keep mutiplying and spread throughout the skin if not treated. Your vet should also treat with Ivermectin until at least 2 negative scrapings are taken. Some breeds cannot take Ivermectin though so check with your vet. Good Luck