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 outermost tube (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 on the lower end of the innermost tube (30). The nested assembly of three telescopic tubes (26, 28, 30) can be controllably extended and retracted by controlled operation of a hydraulic ram or other linear actuator coupled between the outer tube (26) and the inner tube (30). Each of the tubes (26, 28 & 30) carries a respective one or two pairs of inflatable packets (40, 42, & 44) that are normally uninflated and lie 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 a bore. When the bore is at its full depth, the packers (40, 42, & 44) are inflated to force the packers into penetrating engagement with the seabed (100) surrounding the bore, thereby anchoring the ROV (10) to the seabed (100). The seabed anchor (20) allows the ROV (10) to be firmly anchored onto the seabed (100) to resist upward reaction forces arising from ROV-carried geotechnical tools and/or sensors (e.g. a soil sampling tool) being made to penetrate the seabed (100). The seabed anchor (20) is particularly useful for ROVs 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.