whilst at the scottish bike show i bought a product called 'seal a wheel'. similar to slime in the way it works but they guarantee no punctures for the life of the tyre and its not speed restricted. suitable for tube or tubless tyres. paperwork says the biggest puncture it can seal is 12mm diameter. thats a big damn hole.

http://www.sealawheel.co.uk/

i have no connection other than having bought some.