They're helping you clean up the yard!!
I'm laughing because I have the same problem with my female Lab. We call them "poopsicles". I try to pick up after my dogs as soon as they've done their business since I don't leave them in our yard unsupervised (we live right next door to a park and kids used to attempt teasing them).
I was told that it may be because they're not fully digesting their food (we feed MediCAl) and it still smells good to them once it comes out the other end
We've tried charcoal biscuits (it's supposed to smell bad once digested) but it doesn't deter Penny once it's frozen. Maybe they'll work for your dogs? Feed them 1/2 a biscuit 10 minutes or so after every meal. Hope this works for you.