i have seen fabricated belt "retainers" made from [approximately] 1/2" round stock with a flat strap welded to the back that bolted to the water pump/alternator to keep the belt in place at high rpm.
when the belt would rise up out of the groove, the round stock "retainer" would rub on the top side of the belt, keeping it in place. these were placed approximately 1/8"[or a tad closer] above the pulley[s] after the belt was installed and properly tensioned.