Slip catching is a hard skill to practice with realistic movement, but your ground's light roller might just be able to help.

Throw balls onto the top of the roller (with a bit of water to reduce friction) and see how realistic deflections can happen. The ball can both fly off and die on you, just as would happen in a real slip situation.

Watch a short video demonstrating it here.

It's best to use old balls as they tend to get destroyed very quickly. We also had good luck with soft bowling machine balls, incrediballs and hockey balls (the last one if for the very brave as the ball is hard).