I've had "yard" flocks and commercial flocks raised for meat-eating and egg production. Chickens react to the color red best. Which is why in brooders (or the coop) if they see blood they will literally peck to death whoever's bleeding. This is why commercial brooders de-beak chicks. And it's why they will ruin your tomatoes ; ))

As for allowing them to free-range, nothing is off limits to them, including decorations, insulation, etc, etc. They will peck out of curiosity, and then sometimes it simply becomes a habit (non-food related) so they can quickly ruin stuff. And it's funny what they will like and not like. I've found this varies from flock to flock and from year to year, and think it's because of subtle differences in feed nutrients. I would never let a flock near anything I wanted to keep nice. As BEG said, even if they don't destroy the plants, the way they love to dig, scratch, and dustbathe, they can make some serious holes in your landscape ; )) Plants they disregard in the summer may become a new focus in fall.

For our yard flocks (I always had to have some chickens up close to the house!), we used electrified netting. It's almost invisible, mostly keeps them where you want them (mostly, because some will fly over occasionally), and is easily moved. You can see what I'm talking about here at Premier1. I know this may be a pricey solution, but our fencing lasted about 10 years before it needed to be replaced and it meant the chickens stayed where I wanted them–with the added bonus of protection from foxes and raccoons.  

btw, they seem to not like four o'clocks…until they bloom. ; ))

The only chicken-proof plants I've found so far are either plastic or concrete.  My chickens will eat anything.

Liz, I don't mean to hijack this thread, but I have a real dummy's question about the electric fencing, since I haven't seen one in person. How do you get in and out? I didn't see anything like a gate, so do you have to move the end posts each time?