If you don't want your chickens on the porch or in your flowers, you'll have to fence them OUT. Four-foot high 2" poultry netting supported on rebar posts (which are easy to drive into most any soil and also easy to pull out again) works very well to keep even the flyers in or out. The trick is to use netting with thin-enough wire that they can't figure out where the top of the fence is and therefore have nothing to fly up onto or over, and the sort of 2" poultry netting sold at Home Depot or Kent or any home improvement type place is just the ticket. Even three or two foot high netting of this type might work for you. It all depends on how ambitious and determined your birds are.
More solid fences or those with readily visible top lines on them, like a kennel panel made with a framework of metal tubing or latticework with a top rail enclosing a deck. typically need to be higher to keep out determined chickens that can fly some, at least six feet, and even then some will just cackle-laugh at you as they sail up and over without missing a beat. Having something irresistible on the other side, like juicy red ripe tomatoes, is the most problematic. I'll never forget how I once thought years ago that I'd foil my new chickens by--hey! using some spare kennel panels to fence in my tomato garden! Six-foot high panels, too... The white Leghorns got in with no problems at all, of course, as I found out the first time I discovered them inside the tomato 'pen', merrily trashing the wonderful new place of heavenly eats which I'd made for them. If they hadn't all been such good layers and such scrawny little things without much meat on them, I might have had chicken dinner that very evening to appease my rage.
You can also try using flat rocks or beach stones as 'mulch' if your chickens wind up leaving certain plants or shrubs alone, but start digging up the soil around them. I'm dealing with this right now because my own chickens now have access to a couple of rugosa roses growing in small raised beds on a gravel terrace. I'm using the flat rock method to protect the enclosed soil which the birds would love to turn into new dusting sites and I'm sure that aside from losing a few low-growing flowers off the bushes later on, that the roses themselves will be fine. Of course we're talking about big mature bushes here. I wouldn't trust the chickens with little two-foot high bushes and would fence something like that off because I know they do love eating those rose petals...