i used a normal jubilee clip but make sure the screw doesn't foul anything
i'd be surprised if the boot had split, it's very common for the clip to break and the boot pop off. A good quality clip is necessary though, no cable ties!!!
What's wrong with cable ties? I cable tied both mine a while ago cos dark black grease was leaking out of the sides of one and spaying on the insides of the wheel.
Vish it just looks like that cant see no split in the rubber, what grease would u use?