Quote:
Climbing-  Yes- I had heard alligators could climb, just had a hard time believing it.  Here is a web site 
http://edis.ifas.ufl.edu/uw230 and an excerpt about climbing.   "Myth #3. Alligators are not good climbers.
Alligators have sharp claws and powerful tails to help them push their bodies up. Young alligators are agile climbers and adults have been known to climb fences to get to water or escape captivity. Low fences, therefore, may not be sufficient protection for pets in areas where alligators are present. Fences should be more than 4.5 feet tall if you are attempting to keep alligators out of your yard."
Sense of smell-  I did a little research on the alligator's sense of smell.  Indeed they have a keen sense of smell- even when submerged in the water an alligators eyes, ears and nose are visible and they do use their sense of smell for finding prey.
Hunting on land-  Here is what I found about alligators hunting on land.   "Although fish and other prey taken in the water or at the water edge form the major part of alligator's diet, adult alligators also spend considerable time hunting on land, up to 50 m (170 feet) from water, ambushing terrestrial animals on trailsides and road shoulders on warm nights." from^ Dinets, V.L. (2011). "On terrestrial hunting in crocodilians". Herpetological Bulletin 114: 1518
I personally think that if an alligator were to have line of sight to chickens they would naturally be considered prey, so I would build an enclosure with that in mind. 
Again, for many reasons I have decided not to take my beloved hens from Idaho to SW Fla.  Though i will be forlorn for a time without them, they will continue to live a carefree life in the manner to which they are accustomed.  Once I have gotten settled and experience life there, then I can make an informed decision about keeping chickens safe and happy!