I have no lawn mower (no grass) and the cable run would be where no spade would be used (along a wall on concrete) This would be a semi permanent thing as the heater would only be used as a frost protector. I always use a RCD with outside electricity. I want to leave the cable in its position, and read that ordinary cable is not suitable for outside use, hence the suggestion of using hose. When not in use the house end would be unplugged, so I dont see why a permanent fix by an expensive sparky would be required, regardless of building regs (no offence intended) as its no different to using a lawn mower outside.