I want a paint that's safe, what should I look for or avoid?
His paws are getting all rough and sore so the paint will help smooth it out I think.

I think it is a great idea to paint the floor! Concrete that is unsealed collects all kinds of stains and smells, so it can become an unhealthy environment for your dog.
You will need to clean the concrete first, though, or the paint will not stick to the surface. Meriatic acid would do well in this case. After it is clean, go and get yourself some good quality concrete primer and paint. You could roll it on, and the surface will become much smoother. Don't paint in unfavorable weather conditions and follow all the directions on the paint can.
If you let it dry properly, you should be able to hose it off just like unsealed concrete to keep it clean.

Weather conditions will cause the paint to wear eventually, so it will need to be painted periodically.

Ask where you buy paint. they will be able to tell you the best paint to buy.

Before you go to the trouble to paint, you might want to try this stuff called Pad Heal. You "paint" it on your dogs pads and it conditions and protects their pads. It's made for sporting dogs, but you can use it for something as simple as rough feet from concrete floors! Check this out:

Never Paint Your Dog!!!! Imagine If U Were Ur Dog And Someone Was Painting U!!!!!!!! Meanie >

why paint?