(Repeater Term) A condition experienced on VHF and above where a signal rapidly fluctuates in amplitude causing a sound akin to rubbing a stick on a picket fence. If a repeater user's signal isn't strong enough to maintain solid access to the machine's input (such as when operating from a vehicle passing beneath underpasses or through hilly terrain), the signal would be hard to copy because of a pronounced, rapid fluttery or choppy characteristic.
We can't copy you, you're picket fencing really badly.
In competitive forensics, to picket fence is to recieve only scores of 1 (the highest score) in all speech rounds.
Sarah: How did you do at the Jack Howe tournament?
David: I picket fenced it!