German Shepards on Pogo Sticks

Garden walls here are made of galvanized corrugated iron - about six feet tall, give or take 3 inches.  This morning I went for a walk in the fresh morning air (two and a half dozen flies attempted to go for an inhale, but we won't go into that here).  After a good solid meander I paused on the edge of an alley beside a playing field to check my bearings.  I became aware that from somewhere behind me i was hearing a low, breathless "Woouufff"-ing noise, and a regular heavy thumping, like this:
"Whooouuufff-"
*thud*
"Whoouuf-!"
*thud*
"Whouuffff-"
*thud*
I turned one hundred and eighty degrees and found myself nose to nose with a garden fence.  Over the TOP of it, appearing at intervals of roughly five seconds, were the head and shoulders of a very very large German Shepard dog.  There was a very definite forward element to his attempted trajectory, and to all appearances, he was made mostly of teeth.
I could not honestly say if the teeth were intended as a statement or simply a by product of breathless leaping, but the animal was not tiring out in any way or shape or form, and I didn't stick around to investigate.