Ceri JC

I'm not expert on the matter, but if it was on a lawn by the kitchen window, I'd say you have two options. Either a wall mounted ground anchor under the kitchen window, or digging a trench in the lawn (a rectangular one running along the next to the wall would probably look tidiest aesthetically), filling that with concrete/cement and the ground anchor set in that. Be aware that if it's a big hole you're setting it in, the ground anchor may well sink down a bit into the concrete as it sets and not wind up level with the floor (not a huge problem, but doesn't look too tidy). You could either put some gravel under the bit where the ground anchor itself will go, or part fill the trench to the level where the ground anchor would go down to and let it set, then do a second layer with the ground anchor in place.

Oh and of course you should make the area of cement/concrete big enough that it can't just be lifted out with the bike. One other thing you could do to make it look a bit tidier is set the top of the filled trench a bit below ground level, then re-cover most of it (just leaving a few inches around the ground anchor bare) with the turf (make sure there's enough soil on top that the grass won't die in the heat). Effectively, the base the ground anchor would be set in would extend out horizontally below the surface of the grass.