Surely you should use them as a flower pot or something? Spray paint them gold and donate to MTBO to use as a valued trophy? They're certainly built to last.
(In fact, I have my original MTB shoes from 1998 still, they get the occasional outing but have only ridden in Australia, all states bar NT and SA).
More chance of ending up as a dog toy, especially if they were left in the garden. Ideally I should've found a trail called 'two shoes' or something to leave then on as a decoration.