The clone stamp is not your friend, it's not anybody's friend, it's evil and should not be trusted.
No seriously though, there's better ways than trying to clone the whole thing convincingly. Try using content aware fill to get rid of those gators in the background instead. Photoshop will calculate the content for you, make a seemless transition from the edit to the real image, and do it in the blink of an eye. This is a good photo to practice it on. All you do is use the lasso to draw a marquee around what you want gone (the gator) and then hit shift+f5 to bring up the fill menu, change the Contents dropdown to say Content-Aware and hit OK. Photoshop will do the dirty work for you. You'll have a slight imperfection where the gators head was blocking the edge of the post, you can use your clone brush to rebuild a fencepost where his head is. Select your clone stamp, option+click to set your target on the fence post with your brush centered right on the corner of the post so you've got a clear reference point. Then line up below it so the corner of the post continues straight, draw in a little post action & wham bam thank you ma'am. You've got a seemless edit.
...more than one way to skin a gator.