Theft resistant upstanding mounts adjustably support at temporary, often unattended outdoor locations, such costly devices as compact, wireless electronic devices that control such excavation machinery as bulldozers and road graders. Each mount is connectable to or includes a massive base structure, and includes an upstanding, telescopically extensible mast. Lockable connections are provided between many components of the mount. A lockable, swivel connection provided between the mast and a costly device supported atop the mast permits leveling of the costly device for proper operation even if a longitudinal axis of the upstanding mast deviates significantly from true vertical. A protective cover locked to the mast assembly denies access to a control knob that might otherwise be used to detach the costly device from the mast.