。。
Hold on. That's not going to fly.
Literal
Hold-on. That-way [not-gonna-go-そうはいかない] [emph-よ].
どっこい is an interjection used to pull someone up short — 'hold on / wait a minute / not so fast.' It can also be an exclamation while bracing for physical effort. そうはいかない (literally 'it won't go like that') is an idiom for 'that's not going to work / that's not how this goes,' rejecting an implicit proposal or expectation. Both phrases are on the older/rougher side of casual speech.