https://www.quora.com/How-deep-should-I-bury-a-body-so-it-doesnt-smell-while-it-decomposes
I googled “how deep should a body be buried so it cannot be smelled”
Above answer from Texas law.....18inches in a metal container, 24 inches in a wooden or no container....but it can still smell
However reading many articles, there are cemeteries that give off odors for various reason (broken cement containers, boxes, no boxes, vaults issues). Also not all countries have laws to bury the dead. In the USA each state has its own laws.
So, IMO if he did bury Jennifer, he would have dug a shallow grave as he did not have a lot of time nor would he want to spend a lot of time digging. He would not think the body smelled, but IMO it would have smelled unless he put it in a container. Then only a trained dog would be able to smell it.
I wonder if LE searched the yards of any homes being built for a shallow grave, or under a newly laid patio. If he buried her in water it would be in a container full of cement to stay at the bottom otherwise the body will float to the top.
I still hope Jennifer can be found.