I'm sure "postie's sheltie" has to be correct. I put the [?] by "postie" in hope someone would tell me, a non-Scot, what a "postie" is. I think probably "haud awa' the smell," which is how the DT has it, is probably correct, rather than my version. McColl's orthorgraphy is sometimes extremely odd, and I don't believe crofters usually had mills. But as you say, what do I know question mark.

I first heard the song on McColl's Bothy Ballads. But that was 40 years ago, or so, and I don't recall exactly how he sang it.