Sounds like you need to invest in a sturdy lid

Clever skink: My big caramel northern learned how to fall safely. I'm impressed, but none too pleased.
Story:
I was vending at a reptile expo. Jenga had been locked away in a bin all day where he could be seen, but couldn't get his mouth onto any passing fingers. He was bored. When it slowed down, I decided to take him out for a bit. I tried putting him on the table, but he kept trying to suicide-dive and I had to keep catching him. I decided it was high time he learnt that falling wasn't fun, and that I wouldn't always catch him. I usually do this at home by letting them fall short distances onto soft-ish objects. They get a start, and it seems to make them think twice about suicide-diving again.
At this expo, I sat in a lower chair and let Jenga on my lap. He looked down, and dived. Hit the floor and got a start, as expected. Back on my lap. This time he spent some time walking around peering over the edge. Yay, progress. Then he dived again. Again, he seemed a bit stunned by the fact that he hit the floor, and back up on my lap he goes. He spent a good 15 minutes quietly looking over the edge. He wanted down, but falling wasn't so fun now that I wasn't catching him. You could practically hear the wheels turning.
Once again, he dived. I rolled my eyes. Except instead of belly-flopping, the bloody genius used his stubby little legs to lessen the impact. No impact mean he wasn't stunned. Not being stunned meant he was free to run for the hills - with me hot on his tails trying to catch him. I did of course, and he went back in the bin. He's too clever for my own good. Never trust a skink.