For us to answer & be of help, a bit more info would be nice. What are you housing him in? Trying to picture the "top rim"...is this a glass tank? If you actually give him some branches (wedge them diagonally from 2 or more corners so the cross in the middle) he'll have something to actually hang onto so he won't fall, or at least be less likely to fall.
What are the temperatures in the enclosure? lowest, highest? If it's too warm, that may be a reason he wants out. Or else he's hungry...are you sure you're feeding him the right size? (again, we aren't seeing him or what size you're feeding him...hint hint)
You are correct that it's better if snakes do not keep falling. While now & then is usually no big deal, it's better to address possible reasons for this & prevent all you can.
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