My husband said, "really? really? you're going to write about that?". Yes, I know it's a gross topic, but it's a very common ailment. I would say the general practitioner's "bread and butter" is allergies (ear and skin infections), anal glands and nail trims. These are just the things we deal with.
My hubby asked if I was going to use one of my favorite food analogies to talk about anal glands and I informed him, I do have some standards for sharing on the internet...
The anal glands are small "scent" glands on either side of the rectum. They are present in both dogs and cats (although thankfully, they are rarely a problem in the latter). As a dog defecates the scent/fluid gets released from the glands and leaves a type of "postcard" of where the dog has been for other dogs to smell (like the marking behavior they do when they urinate on things, especially males).
In cases of allergies or lower gastrointestinal (GI) issues, the above process does not work as well and the glands can get "backed up". This can happen to the point that the enlargement of these glands causes great pain, can even obstruct the dog and even form painful abscesses (infections). If your dog is scooting, licking at the hind end or having pain defecating, definitely have your veterinarian look at the anal glands. This issue is so painful and uncomfortable, I have seen it misdiagnosed before as a herniated disk (when it was really the anal glands). The difference between back surgery and expressing anal glands is pretty big, but to some dogs, the pain is similar.
The best way to prevent anal glands from impacting is to treat any underlying allergy or GI issues and feed a diet that has plenty of fiber. I sometimes even recommend a teaspoon to a tablespoon of canned pumpkin in their food to help keep things "regular".
Sorry for the gross topic, but like I said, I see this quite regularly and it is something to be on the lookout for.