Sorry, I addressed the last first.
If the inflammation from the grass allergy was severe, then calming the skin down with depo isn't bad medicine at all -- sometimes you NEED to.
Yes, I've had several dogs with atopic allergies, but grass allergies can come in two types -- "atopic" (inhaled -- which in dogs also means it's transmitted thru the skin) AND "contact" allergy -- and when you say there were pustules on the belly (they can look like little tiny blisters) that leads me to believe contact allergy.
If you live where there is St. Augustine sod (well known anymore for holding water so it grows a "lush" lawn in hot southern climates). Also wandering jew, night-blooming jasmine, poison oak -- all of them cause contact allergies. Yep - just like poison ivy for people.
Aloe can help sore skin. (not an aloe cream -- but the aloe harvested from the aloe plant itself).
Given the contrast between the two dogs -- and touch base with this vet on this idea -- I would have him tested for thyroid. NOT with a regular lab -- don't waste your money. But rather either send it directly to Dr. Jean Dodds, or send it to Michigan State's lab (she built their lab and they use her protocols). The idea is a regular lab uses the same 'scale' for ALL breeds -- and it just doesn't make sense that a min pin is gonna have the same 'metabolism' as a St. Bernard, or a bassett or a saluki! Not size -- metabolism.
If the dog has low thyroid it's not going to 'cure' anything -- but it can level the playing field a bit. I've got a cocker with low thyroid -- and a year ago I just couldn't keep his skin on his body -- trust me, I've done it all -- home cooking (no grain), elmination diets, frequent bathing, Chinese herbals, and absolutely exhaustive dealings with antibiotics and steroids. *sigh* Allergies ARE an immune problem essentially, and you use antibiotics and steroids all the time and you're lowering the immune system besides all the bad side-effects.
Finally found the thyroid problem and wow -- the allergies are there but DO-ABLE!! What a difference!
Tape worm -- could be the raw meat. But also -- you're getting a little misinformation here.
They don't have to 'eat fleas' like a meal. All it takes is ONE flea. That's all. One flea that hasn't had a chance to die yet! And if the dog gets walked outside he's gonna see an occasional flea.
However, that being said -- tapes are TOUGH to get rid of. Because at the "other end" of all those segments that break off (all you see in the poop are segments --pieces that have broken off from the tape worm and sometimes you can't even find them in a stool sample!!), but at the other end is the 'head' and that is imbedded in the wall of the intestine somewhere. The tape medicine may kill the segments and leave the head still alive to re-generate.
So a few months later, the tapeworm has grown long enough to finally shed segments again. So if you treated a 'few months ago' it's likely you just didn't get the head. And every time you treat that head may get just a wee bit more 'resistant' to the drug -- so make SURE that vet knows you've dealt with this before.
Allergic to mites - that's like saying "allergic to spiders". I'm not being sarcastic -- it's just that there is a lot of misinformation out there. "mites" are arachnids (yep, they are actually part of the spider family) and there are a bunch of them. There are cheletelia mites (and I bet I spelled that wrong) like chiggers, ear mites, sarcoptic mites, walking dandruff mites, and demodectic mites. Each one of those things is called "mange" of one variety or another -- altho sarcops and demodex are the most common to be called 'mange'. Sarcoptic mites (scabies in people) are the 'catching' ones -- they feast on warm-blood -- so they'll bite anything warmblooded. Demodex mites eat skin and hair oil -- found primarily in puppies.
Sarcops and demodex both are very immune related. Sarcoptic mites prey on dogs with a weak immune system (old, young, sick animals). Demodex often hits puppies before their immune system developes but the sensitivity to the mites is a genetic flaw that involves a weak immune system.
At the age of your dog, let's hope it's not demodex. I doubt it is -- it's in the wrong place, the wrong symptoms, wrong age of dog, wrong "presentation" entirely.
Yeah, I know a lot about mange *sigh* -- my husband doesn't call me the "Mange Queen" for nothin!
The one question I would ask you specifically (because sarcoptic mites can be tough to diagnose and your description of the unrelenting itch makes me ask this): Are YOU itching? Do you ever feel like "gosh, he's got ME itching" or do you have any unexplained small red rashes or tiny pustules??
The second dog's immune system might be strong enough to throw off sarcops, but typically a human's isn't.
Sorry, this is a lot but I hope I covered everything. You adopt dogs with weird allergies? I'm convinced I have a secret-but-HUGE-blinking invisible-sign-only-seeable-by-dogs that says "Skin problems? C'MON DOWN!! and the food's good here too!!"