Potty Training my Chihuahua?

I have a 17 month old Chihuahua who has been neutered and was doing great at potty training. We started with crate training and then we let him out of the crate after about 10 months and put a box by the front door with real grass in it in case he had to go while I was at work. This has been working great then my 4 year old Chi started pooping next to the grass and the 17 month old started marking anywhere and everywhere.

We then put in a doggie door hoping this would help. They do go out side to poop and most of the time pee, but the little one is still peeing and will do it in front of me. The older one only in the morning poops next to the box. I need help. I have even removed part of my carpet he were he would pee, but he will pee on tile too.

By Wanda51