lol, was good to meet you too. Water D's are very random about where they lay. Normally in a part of the enclosure that has full sun. Problem is that eggs can fry if sand not deep enough. Strangely they seem to like laying in open areas once they have dug a hole rather than under rocks etc.
Best way is to have an area where the sand is moist and deep. Depending on the type of sand you may be able to tell where they have dug, however they cover it up well.
Also a good idea to weigh the females around breeding time in order to work out if they have or have not laid- but you will need to keep them relatively tame or they will bite----trust me.
if you remember K's big enclosure, he had only one sand area in which they could lay. This was a good idea which will save him fossicking around for hours, or days.
Good luck, that is an awesome looking set up. Woulod look great with some shinglebacks