Having just read this revived thread in its entirety, here are a couple of variants on sayings already noted, and one observation on "Hector"/"Heck".

"Were ye born in a field with the slap open?" (when someone doesn't shut a door)

" 'I see, I see,' said the blind man, and he didn't see at all"

"A blin' man on a flying horse would never see it" (said when there's a small flaw in a piece of workmanship). In Donegal, I've heard a rough, crude, hasty, improvised, makeshift, botched &c job being called a "half-hanged McNaught" (pronounced "Micknyat"), apparently after someone who was hanged but revived later - anyone got any further details?)

"He'd drink porter through a Polisman's sock" (i.e. said of someone with, like Tim Finnegan, a "love of the liquor"; Polisman being an officer of the law)

Not dissimilar is one collected in "The Patter" (an anthology of Glasgow sayings), "He'd eat a scabby dug", which as the editor put it, meands that someone is extremely ("not to mention indiscriminately") hungry. There's another variant, "I could eat a farmer's arse..."

Staying with dogs, notice the original mention of Hector has him as "a pup". While of course a human child might be called a "pup" - in fact, I've been jocularly called a "cub" myself - and Hektor, Prince of Troy, might well provide the name for a mastiff, like Caesar in Burns's "Twa Dogs", there's the seventeenth-century Scots poem, the Elegy for Bonny Heck, a famous greyhound from Fife.