Learn from my mates experiance, he has 18" wheels on his car which were just scrubbing so he decided to "roll" the guards, thats the little rolling tool they use to lip up the inner lip of the guard.
AVOID IT!!! his guards buckled under the pressure and now are rippled, this also weakens the guard too. Just incase you were thinking bout that rally look. If you want to fit 18"/17" wheels, keep them to a 7" with, this will give enough clearance and let you lower the car without having to work on the guards.
His car is GTi but im sure this will apply to all 206's .