"HeyBub" wrote in message
A client wants me to put somethng on a concrete curb to keep the
rollerbladers from using it to practice.

Whatever you do, it must NOT be for the primary purpose of harming people
who have a lawful right to do what they're doing.

Your modification can be decorative or functional, however, with the
downside of "discouraging" roller-bladers.

Bolt-on garden gnomes and Burma-shave signs come to mind.

Something else to consider. Who owns the curb? If it is city or town
property, he can probably do nothing. If it is his own private property, he
can get rid of the skaters by normal means for trespassers.