Static defenses, experiences?

[bluegaspode]

Most bots coming your way won't know your hill location until they stumble on it, regardless of algorithms for symmetry detection (maybe I'm wrong)

Nope! Generally, you can deduce every single hill location once you've seen even a single hill of one player.

For this map this wouldn't work, correct?
http://aichallenge.org/map.php?map=maze/maze_04p_01.map

If you find just one other hill to the left or right you know that the map is reflected, but don't know if there is another reflection to the south (or just a translation) for hill #3 +#4.

But generelly I agree - as soon is there are rotations or just translation one can easily know the position of all other hills, just by finding a single one (like on the map you had).

[Parasprites]

That's why I said "generally". It's only true if the symmetry group is cyclic and the hill you find is a generator. But this is the most common case.