My son's pit bull will spend hours in the yard and then come in the house and defecate on the floor. How can we break that habit and get him to use the grass?
You don't mention if this is a change in behavior or if this has gone on the entire time your son has owned the cutie, but if it's anything different from what he's always done, it would be wise to start with a visit to your vet. Animals can't tell us when they feel off, and the only thing they can do is act differently.
It's common for dogs to have a preferred surface for bathroom needs, and city dogs tend to be more comfortable with cement than soil — it's what they have easiest access to. Assuming he's healthy, this is likely what you're dealing with here. To help him make the adjustment, keep a close eye on him inside and take him out as soon as he starts showing signs that he needs to go. When he does have an accident inside, rather than just tossing it, put it out in your yard in an approved place. Next time you take him outside, lead him right to that spot, let him notice it (don't push his nose into it; just lead him nearby and his nose will find it from there), and praise him. That will build an association in his brain that outside is the place to go. When you go back to the scene of the crime inside your house, make sure you're cleaning thoroughly with products specifically for animal waste so he can't smell it anymore. Your neighborhood pet supply store should be able to offer suggestions.
This week's expert is Amie Glasgow, behavior and training coordinator with the MD SPCA. Send questions to email@example.com.