Having done this quite a few times with very successful results on quite a few brands of tyre i though i'd pass this tip on.
Have you ever got a slice in a tyre from a piece of glass or other unknown object that has left you with a substantial split in a tyres outer casing. Well instead of placing a patch inside the tyre or buying a new one, which really is a pain when the one you got is still quite new, try this instead.
Deflate the tyre and clean out the slice with some rubbing alcohol, then you will need to go to a hobby shop and buy some of the modelers 'super glue' as used for gluing the parts of model planes etc.
I have had very good success with a brand called Flash or Zap, the type to buy is medium gap filling formula, this is so it can cure a bit slower and fill any small discrepancys in the area.
Do not buy the generic stuff from regular stores since they usually dont last long and really dont work anyway.
The modelers glue is supposed to work even on oil soaked surfaces,this happens with the fumes from the castor based oils the planes use for the engines as a lubricant, and since the tyres use a release agent to help remove them from the mould this also tends to be an oily residue impregnated into the rubber.
Now squeeze the glue in a SMALL drop into the split and hold it together carefully till it cures, this is usually about 30 secs to a minute tops. Once its cured inflate the tyre to about 50psi and leave it till your next ride, then inflate to your regular pressure as normal before you go riding. If its all happened correctly the split should not reopen again, well at least none of the ones i did have ,,,, yet, and its been quite a while, at least till the tyre finally died.