Pooping in the house

Question
Hi, I have 2 labs a yellow male lab named Buster and a black lab named Bella. Buster is 18 months old and is neutered and Bella is 6 months old and is spayed. The problem I am having is both of them have started pooping in the house in the last week or so. I have had them them since they were 8 weeks old and potty trained both easily, but now it's seems like I will take them out to go potty and they pee outside and I do give them enough to poop outside, but no sooner are we inside after peeing outside they will poop in the floor. I used umbilical training with both and I still continue to do it. Also, when they are not able to be watched I crate them separately in their own crate. When the do poop in the house I normally try to catch them in the act when I do I quickly rush them outside, but they don't finish outside they just sit their on the grass. I don't punish them is if I fail to catch them in the act, but if I do I sternly tell them bad dog and show them what they have done. I don't know what else to do?

Answer
I don't have a quick, easy answer, or even a sure one.  Try too learn their schedule.  When you thing it is near the time for one to have a bowel movement, take it on leash.  Walk around.  They can only walk and hold it so long.  When it finally has to go, lavish praise on it.  They may catch on eventually.