I would expect they have, are and will analyze and grid search, satellite search, drone search, dog search, metal detectors, sonor, gpr, full shebang and gut that whole property if they need to. What they accomplished to unearth these boys up to this point has been amazing. And now they especially know what his potential preferred method of disposal is if there are other crimes. They're searching with all their resources, I believe there are many, the scope is huge, they wouldn't just walk away, no way. This is a serious serious investigation and they know it. There are multiple competent agencies, manpower...I don't think any warrant conflicts occur here, 4 bodies is all the probable cause they need.
Hopefully we will see them searching the area you have a gut feeling about.
Eta: I would also think "perimeters"...if so that could be tricky, how fAR off the perimeter...as Tim Miller founder of Texas Equusearch said one time with reference to Terrilynn Monette's case, "off an inch, might as well be off a mile...")
I feel a lot better having read this post, thank you. Things will also likely be a lot quieter in terms of searches now so we may not know unless locals see/report things going on. Have the media all pretty much left the area since the confessions and recoveries?