Dynamite or black gunpowder works very well... it's just that getting the precise amount is tricky...
A good, sharp utility knife (the kind with the replaceable razor shape blades is best... cold water helps clean up blood by the way) will work. There are products called "sealant eater" by various companies, but I've never had much luck with it... some say a spray or two of WD-40 helps, but I've not found that to be exactly true either. Are you sure you really need to remove it?
Thanks for the amusing answer Clanad, we will try these ideas, in answer to your question - yes it does have to be removed for a number of reasons - too boring to go into.