"Doh" is commonly spelled "D'oh" and is used as an exclamation of regret, as coined by Homer Simpson.

You are thinking of "Duh", commonly spelled "D'uh", which is used an indication of ignorance, as coined by Moose Manson (later Mason) in Archie Comics.

d'oh

or doh

http://www.dictionary.com/browse/doh

Oh boy....if you're coming to the rescue, you better make sure you're well-prepared that you don't need rescuing yourself. 

The two of you hugging each other as............ you both sink together. 

Yes, your link backed up what I said exactly. Not bad, considering I was just writing off the top of my head. They didn't get the Moose etymology though and said "Duh" dates to the 1960s. I believe, however, that Moose was using "Duh" as early as the late 1940s.