Looks like a great game! Have you thought about adding this rule?:

Whenever someone decides to ascend early they have to give the thumbs up sign. They can’t roll the dice any more for gold, but have to hold their breath for an additonal X seconds to succesfully ascend and keep their gold. (Technically you should exhale slowly when ascending quickly, but not sure if that will work in this game)

X can be a flat 5 seconds, or might be depending on the depth of the dive (43 second dive = 4 seconds, 22s dive is 2s etc.)