Anal Gland....Thread like.

 The first thing that comes to mind is green beans. Since I started giving my pups green beans we haven't had a problem and the same for our neighbor's pup. They love them frozen too, just watch out for salt if you use canned. I found frozen the easiest to use in their dinners, just have to microwave them for a few minutes.

 The beans are a good idea.  Maybe try a different brand of food and more vigorous exercise.  I've also had good results when having the vet and two of his assistants try to trim Pipers nails.  Everything gets sprayed on the wall.

The biggest thing that will help is for you to learn how to express the glands yourself.  Done regularly, before impaction develops, expressing the glands while there is still fluid in them will give the dog much relief and solve your problem.  I once had a border collie mix who came to me with impacted glands.  I learned how to express her glands myself.  End of problems.  She never impacted again.

I can explain the process.  It's really easy.  A little messy, yes.  But easy.  But, really, you should have your Vet show you how.  Unless your Vet is just plain greedy and wants your money every time it needs to be done, they should be williing to show you how so you can do it yourself.  All you need are cheap disposable gloves (bought at any pharmacy), K-Y jelly or some other lubricant (also bought at any pharmacy), paper towels, and someone to hold the head of your dog.  Eventually, some dogs let you do it with no one holding their head at all.  They somehow know you are helping them, and don't give any struggle throughout the process. 

Please, learn how to do this yourself.  You will be saving money and making your dog much happier.