Now we'll work on Guido's leash nub.  We could easily CUT and PASTE the sky over the nub but I want to show you these two other tools because they come in handy when removing collars and leashes. 
  Zooming into the area will make it easier to do.  Select the very versatile RETOUCH tool on the tool bar.  Notice that the TOOL OPTIONS box gives you a ton of choices for the type of retouching.  For our example we can use the SMUDGE or the PUSH tool.  PUSH will take the area under the cursor and use it as a temporary brush.  Allowing you to PUSH it into the are to cover.  SMUDGE works very similar but as you move the cursor it picks up surrounding color.  Similar to finger painting.

I have used the tool to PUSH the blue sky over the nub.  When removing a collar from a dogs fur you can use the PUSH or SMUDGE tool to slide surrounding fur over the collar.  Also note the OPACITY setting on the tool.  By lowering the opacity the PUSH merges colors making it look like a combing job.
    If you are taking a picture and you already know you are going to edit out a collar.  Do yourself a favor and use a fine collar and leash.  Don't be afraid to experiment with the settings.  Remember you can UNDO anything you change and nothing is permanent until you hit SAVE.

Here is the finished result.  I can still change a lot if I wanted.  There is the cell phone tower over Guido's right shoulder.  The breeze was giving him a bad ear day.  I can even add more blue bonnets to fill in the foreground.  I like it like this.  It makes a nice background on my monitor.