Tone Tubes & Legit Target Objects

We have a great piece of land that has been approved by the city to eventually install a basket course.  But until that happens I want to install a temp object course to get the community excited about the notion of a new course.

Can any one point me in the right direction on how to construct a "tone tube" or have any ideas on what some cheap and legit objects or targets are?

[The Monster]

We have a random hole out here, Its called The Keg Hole. Its just an empty beer Keg on top of a 4 by 4 post. its actually really precise. if you barely touch it you can tell

[Paul Novak]

Ha! That sounds pretty bootleg. But if it is done correctly I bet it could work real nice. I would definitely like to see a picture of that.

[The Monster]

I'll see if I can track one down, Sorry i forgot to mention this is not part of the normal course. Its an extra hole built by the locals