Literally my exact experience, man - I tried the usual cam locks and only got one side, then I tried with that tool and it kept slipping. I hadn't worked out that I needed to use a metal zip tie and stubby impact, talk about running the gambit on tools here. Ok, well I gotta go to the store now and get a stubby impact and metal zip tie, I only have a normal impact and plastic zip ties. Thanks!I used one of these when I did my timing belt. It has a tendency to slip off the gears if you try to undo the bolt by hand (I ended up using a stubby impact wrench) so it helps if you put a metal zip tie around the two parts that contact the gears so they can't expand when you put tension on it.
The typical timing belt cam tools will only work on one side, since only one of the cam hears has the large openings that allow them to be used.