Moving at significant proportions of c makes a very brief light show of pretty much any ablative solid, unfortunately.

It's worth doing the maths on, for instance, how much ice at 4K you would need to dissipate the energy released by running into a 5g pebble at 0.2c. It's... not a small volume.

Your comment made me try this out on wolfram alpha. Kinetic energy of 1 gram with velocity of 0.1 C is 452.78 gigajoules. Energy of the Hiroshima bomb is 6.3x10^13 joules. It would take 139.14 grams of matter at a velocity of 0.1 C to have the kinetic energy equivalent to the energy released by the bomb. So wow, yes, stopping even a small amount of stuff at those speeds is no joke.