How do you get paint rollers to stay on?

If the tines (what hold the roller in place) are metal pull outward on the middle of each tine with a pair of pliers.

Another way to secure the roller sleeve to the roller is to wrap something around the roller tines to make them fit more tightly.

I agree with Mogie. I grab the roller tines and gently pull them outward. Another thing is to paint in the direction so the roller doesn't slide off.

The cheapo roller frames aren't designed well. I highly recommend this roller frame! It hold roller on and it has even pressure for the paint across the entire roller, not just on the ends.

All the paint rollers I've ever used have a clip on the end that prevents the roller from coming off, but I really like the ideas seen here because sometimes those pins get lost!

Another word for the pin is "clip".