So, here's the thing.
I've got a Jewel Rio 300 with the corner all-in-1 filter box thingy.
Over time, baby common round snails have got into the filter and live a dark imprisoned life living off the gunk in the filters.
This is driving one of my Yoyos nuts

Anyway, every day he spends about 2 or 3 minutes biting at the grill bars, trying to get in.
Which got me thinking... I've got a ready supply of their fave snails from my small Betta tank.
Could we construct a "loach puzzle", a bit like the ones that the BBC made for the Squirrels (QED... a long long time ago)?
It would have to be -
Transparent
Easy to exit
Tricky to get into
Heavy enough to sink
Chemical and mineral neutral
Able to contain the snails
It would be minutes of fun every day, but it would have to be adapted regularly, they'd suss it out quickly enough if it couldn't be adapted. Different individual lockable panels or doors for example.
Fun for the fish, fun for owners, what more could you ask for?
I'm welcome to suggestions, I'm no design engineer. The Loach Cube... has a nice ring to it?!
Any ideas folks?
Cheers,
Wex