what units can use fougasses, chevaux-de-fries?

[Ishmael]

For chevaux-de-frises, unless the patch(es) have changed something then all line, guard, militia etc should be able to deploy them. That said, I haven't played for a while, so I need confirmation.
For fougasse, only some light infantry/riflemen can deploy them. I think some Austrian Jaegars and whatnot can, and maybe the British elite rifles, but not Spanish cazzadores (sniffle).

[antisocialmunky]

You guys have it confused with light infantry stakes which can be placed in combat. The pointy fence is deployed by Line Infantry along with their trenchs in defense. Light Infantry get mines in defense.

Those fence aren't only good cavalry defense: If you're defending vs an army with no cannons, you can just set them up slightly outside your line infantry range so the enemy units have to jump over it to start shooting and we all know how bad the unit AI is about fences and the like.

[Fisherking]

Line Infantry also has chevaux-de-frises along with entrenchments. Light infantry has the most choice in what to deploy.