Wimpy or aggressive? Fence-fighting and heel-nipping

I recently trained a fear-aggressive Cocker Spaniel who had a funny (or not-so funny) habit:  ignore people and dogs on the sidewalk until they pass, then turn around the instant they've past, and bark like crazy - sometimes even nipping at their heels (or bums!) Basically what this dog was doing was being protective-aggressive, but after the fact to make sure she wasn't in any danger, because she's a little sweetie wimp.

The analysis brought to my mind another common form of canine aggression:  so-called "fence-fighting". Fence-fighting is when two dogs bark at each other from opposite sides of a fence; or more generally, when one dog barks, lunges, or acts aggressively from behind a fence at other dogs, people, or anything else.

I once saw a funny comic strip (which I'm unable to find online; can anyone help me here?) that showed two dogs barking and barking at each other, on opposite sides of a chain-link fence; then the fence comes to an end, and the two dogs shut right up, silent and quizzical, face-to-face with no blockade between them, with little question-marks over their heads, wondering what the heck to do. Then they both turn back to where the fence was between them, and start right back barking at each other.

When trying to explain to the Spaniel's owner the particular combination of fear, wimpiness, and macho-protectiveness that goes into causing butt- and heel-nipping, as well as fence-fighting, I started using examples from the human world.

Did you ever wonder why so many bumper-stickers are angry, violent, and aggressive? Most of the people who have these bumper-stickers on the backs of their cars would never think to say such things to your face, when they're walking on their own two feet down the sidewalk. But they are invincible in their car-cocoon, sheltered and protected and can lash out however they want to.

The same diagnosis probably holds for lots of instances of road-rage; the sense of safety and invulnerability that the car/fence gives allows us to let our worst selves out, without fear of repercussions.  

Ever notice how such an inordinate number of online posts, blogs, comments, and other mostly anonymous internet opinions are violent, angry, even racist or sexist?

Dogs aren't the only creatures I know who sometimes behave like wild animals. Of course, it's still our job to stop them from doing it. 

The only difference is, they have a slightly better excuse for behaving like animals than we do.