How to Safely Remove Silicone Tank Sealant from Rocks?

[Labenator65000]

OK so I botched up my first DIY rockwork project (partially, at least), so I took part of it all apart to reuse the stones. I searched long and hard for just the right smooth, dark river rock, so I don't want to toss them and search from scratch again. Does anyone have any good tips for safely removing silicone tank sealant from rocks? Keep in mind that they will go into the tank and the stones are porous, so I don't want to use any chemicals that could kill my stock.

 

[ocean]

Only thing I can think of is peel it off or sand it off with sand paper or a orbital.

 

[Labenator65000]

I ended up shaving as close as possible with an xacto knife, then cleaning up with a Dremel.