How do I find unique object ids or do I need to?

I have an object called "pebbles"

Whenever I use pebbles it creates an object called "pebble"

When I type "use pebble on pebbles" which is my attempt to add the pebble back into the pile...

I want the pebble I'm adding to be destroyed.

I try using the destroy function and it can't find the pebble I'm looking for.

could you post your gamefile here?

Yeah, it would be easier to see the code to be able to figure out what's wrong.