Get an old car tyre from ATS or somewhere.
Get some old wire fence netting.
Get some bricks and or pebbles, and cement
Tip the tyre on its end. Stuff the wire in so it ‘fills’ the whole tyre.
Fill the bottom of the tyre with bricks/stones. Fill the spaces with concrete.
When it dries, rotate it slightly and repeat the stones/concrete thing.
Repeat until the whole tyre is stuffed with reinforced concrete.
Wrap in polythene to keep everything clean. Finish with Duck tape.
Voila, hight security Polo mint. Around 60kg for a fairly small tyre. You can roll it round to move it but once a bike is locked to it you can’t move it.
There is no small section for a thief to bolt crop.
The rubber protects the concrete from hammer attacks.
etc