Hey peterm,
Interesting you would find that line ....... and now that you mention it ....
I don't know but I guess maybe this would be an Americanism....
in the context of talking..... sometimes when talking with someone who doesn't respond or just doesn't grasp what it is I'm saying, I might say ... "talking to you is like talking to a fence", hence "wasting time with a fence"
Does that line make sense now ?
Or, I suppose I could be quite literal and write ....
did I miss the boat
or am I talking to a fence ..... or some derivative.....
The crux of the verse is I'm talking and no one is listening.
Les