I wouldn't worry about slippage, think about how open the serpetine belt is without real teeth. Tensioner will have to be replaced if the belt is really loose but if it's just a little don't worry bout it.
98.5 SVT
91 Escort GT (almost sold)
96 ATX Zetec (i brake to watch you swerve)
FS: SVT rear sway bar
WTB: Very cheap beater
CEG Dragon Run - October 13-15