Can I Train My Dogs To *poo* Once Per Day?

You cannot train your dog to defecate once daily.  Feeding only one meal a day will help with this and is not good care of your dog.  Can you imagine how hungry you'd be if you only ate once a day?  Dogs, like people, vary individually--some dogs defecate 3-4 times a day others only once.  
Consider hiring a dog walker or neighborhood kid to pick up the fecal matter if this is a concern for you.

I think you are better off sticking to the routine you already have for your dogs and continue to feed them twice daily.

Dogs, are like humans, they use the bathroom just as we do.  If you have a routine, don't change the routine as it can change their behavior and throw their body and routine off completely.  Good-Luck

It is much healthier for your dogs to eat and poo twice a day. If you don't like to scoop poo, I have a suggestion. I put wood play chips in a corner of my back yard and my dogs poo in it and I didn't even have to train them to. It is so easy to pick up and if I don't get to it right away it dries up and practically petrifies - just a suggestion.