What to stick with?

I recently made up a nice little slate cave, only to have my godfathers Skunk + Pakistani loaches knock it down (they're on 'loan' as snail control lol)
But this got me thinking, I wouldn't want this to happen with any of my plecs inside, so could you lots suggest anything to stick the two pieces together at the top?
I DO have a small tube of aquarium silicone, buuut it's quite old, my grandad gave it to me, and I reckon it's all solidified. If there is still any stuff in there, would it still be safe to use?
If not, would normal silicon be okay?
I've heard about superglue as well?

I mean, if I can get a hold of something, I may be able to get a hold of the remaining slab of slate in the garden, smash it up and use it to create something much more interesting lol!

Thanks in advance everyone!

Personally, I would only use aquarium silicon ........ I have heard you can use superglue (even on the fish and snails) but for the amount you would need to stick a cave together you may as well get aquarium sealant.

Never be tempted to use anything else, no matter how little, as it can have a devastating effect on your whole tanks inhabitants.

As for snails, get some assasins. They won't knock anything over, and really do keep them under control.

High Spreebok, I have used 2 part super glue for fixing filter impeller's and small things , just let it cure for 24hrs and give it a wash, as for your cave dilema: I'd go and buy a new tube of AQ safe silicone- same do let it cure properly and give it a good wash and seeing as you have a whole tube to work with you can go crazy on the slab out the back and create something special
J

i make my own caves and just use aquarium silicone best ive found is bondit HA6 really good.

All righty, verdict seems to be to buy new stuff!
Good idea too, I reckon that stuff grandad gave me is about 10 years old lol!

Just bought a 310ml tube, see how that goes!