A group of Minnesota volunteers have discussed this a few times, and we came up with a few good alternatives (by some definition of "good").
My favorite practical option is propping up the cheval de friese as the CDF's "alternative", making a cliff defense. With the CDF, the challenge is getting on. With the cliff, the challenge is getting off. It's easy to implement, and not too significantly different from any existing defenses. Unfortunately it is significantly more directional than the existing defenses- going from the courtyard back to the neutral zone would be pretty hard.
Some less practical options (in descending order from most practical to least practical):
- A "wall" you have to break through twice to defeat, such as two totes stacked on top of eachother
- "Boiling pitch," which is just a bean bag chair that gets dropped on your robot after going through the defense
- A cage with a bunny in it. Whether the bunny is real or fake is up to the planning committee.
- A flat defense with nothing on it, but the head ref has a squirt gun and gives your robot a squirt every time you cross it
- A second low bar, but connected to some propane to create an open flame instead of having flaps
Minnesota teams might want to be careful in the off season
