Pictures of Apple Snail ("Golden Mystery Snail") Laying Eggs

We have two apple snails (sold as an "ivory mystery snail" and a "golden mystery snail") in our small 6 gallon Eclipse tank. Evidently, the golden snail is a female and the ivory snail is a male, and so they mate all the time. In most tanks, this isn't a problem because the amphibious apple snails have to leave the water to lay their eggs and they can't do that when the tank has a lid on it. However, the Eclipse tank has a large dome-shaped lid so that everything (pump, filter, etc.) can be built into it. So, our female has been crawling up into the lid and laying eggs.

This morning, I couldn't find the female in the bottom part of the tank, and so I lifted the lid... and there she was! I've never seen pictures of an apple snail LAYING eggs, so I thought I'd take some. Unfortunately, they came out kinda blurry, but at least it's something!

You can see the egg sac she's laying right next to her. You can see that as she moves backward, the egg sac gets longer.

In the first picture, on another part of the lid, are some of the remnants of an old egg sac that has hatched (before we realized she was leaving the tank to lay her eggs).

Anyone have any ideas about how to prevent the snails from leaving the water? (note: throwing away the tank is not an option) We'd move the snails to our big tank that has a flat lid, but we're pretty sure our freshwater puffer would slowly dine on the snails until they died a long slow death.