I have a Volvo 2 blade folder and believe the prop anodes are similar. Three segments held on with hex head bolts. I believe the main problem is that the anodes corrode at the thinnest point where the bolt is and then break off whist there is still a goood chunk of anode left.
When I change mine annually I apply a coat of antifoul to the outside face of the bolt head. My understanding is that this isolates the bolt from the anode and the sail drive and you get less degredation of the anode at that point. Therefore they last longer. Last two years mine have just about survived the full season. Also if you don’t have a main pear drop anode you will get more corrosion on the prop anode.