A seabed anchor (20) is fixed to and deployable from an ROV (10) for positively anchoring the ROV (10) to the seabed (100). The seabed anchor (20) comprises three nested telescoping tubes (26, 28, & 30). The upper end of the oute (26) is fixed to the ROV (10). A rotary drill bit (38) is carried on the output shaft of a motor (34) that is mounted o of the innermost tube (30). The nested assembly of three telescopic tubes (26, 28, 30) can be controllably extended and retracted b controlled operation of a hydraulic ram or other linear actuator coupled between the outer tube (26) and the inner tube (30). Each the tubes (26, 28 & 30) carries a respective one or two pairs of inflatable packets (40, 42, & 44) that are normally un quiescent within respective recesses in the sides of the tubes where the packers do not interfere with telescopic relative movements of the tubes. To set the seabed anchor (20), the drill bit (38) is rotated and forced downwards into the seabed (100) to form When the bore is at its full depth, the packers (40, 42, & 44) are inflated to force the packers into penetrating engagement with t seabed (100) surrounding the bore, thereby anchoring the ROV (10) to the seabed (100). The seabed anchor (20) allows th (10) to be firmly anchored onto the seabed (100) to resist upward reaction forces arising from ROV-carried geotechnical tools and/o sensors (e.g. a soil sampling tool) being made to penetrate the seabed (100). The seabed anchor (20) is particularly useful for ROV which are neutrally buoyant or slightly positively buoyant, and which therefore have negligible weight (when fully submerged) for holding them down onto the seabed against upward reaction forces.