No river bottoms, or arroyos. Avoid placing the station near trees, power poles- things that sway in the wind. As a rule, you should be at least as far away as the thing is high. Check the drainage. A vault should be designed to prevent casual entry by kids or curiosity seekers.
Real thievery is prevented by a watchperson and building a very discreet site.
Private landowners are much easier to make arrangements with and the site will generally be more secure. The solar panels can be visible as a shiny object from a long way off to the south. If they are on a tin roof, mostly horizontal, or south of the main road they will not attract as much attention. The principle of this design for broadband sensor vaults is to minimize temperature changes, and to distance the sensor pad from the surficial layer which tilts due to temperature, precipitation, solar insolation, wind, etc. Nearby sources of ground noise, like footsteps and acoustic noise, are also reduced by shallow burial.