For the first time since he took over the Wallabies in May last year, Deans finds himself under something akin to a blowtorch this week.
The similarly-patchy All Blacks are in town, and if they win at ANZ Stadium on Saturday night they retain the Bledisloe Cup with two tests to spare and officially kill off the Wallabies' slim Investec Tri Nations hopes.
Slack, in his column in Brisbane's Sunday Mail newspaper, lauded Deans as a good coach and said he'd had an "armchair ride" in his first 15 months after his outstanding success with the Crusaders.
But if the Wallabies follow up their away losses to the All Blacks and Springboks with defeat at their home fortress on Saturday, the critics will fast emerge.
"The honeymoon has wound down. No more pina coladas and cuddles. There's a mortgage to be paid and a house to be kept clean," Slack wrote.
"Deans does not need to be informed of this. He took the vows and knew the responsibilities.
"'Do you promise not to lose the three opening Tri Nations games of 2009?' was probably not one of the direct questions celebrant John O'Neill posed as the ring was put on the finger back in late 2007, but it was as good as understood.
"Defeat against New Zealand on Saturday in Sydney equates to a broken promise and once you stop trusting, a relationship can deteriorate rapidly. "
Against the Wallabies' big two opponents, Deans is 1-4 against the All Blacks and 2-2 against the Springboks.
Slack said the team under Deans had won enough games against other opponents, "with just enough panache at the right times to ward off any major inquisition".
Deans' defence system was largely solid, but the key factor missing was the ability to seize the critical moments in a match.
"The Wallabies struggled occasionally when the heat was applied last year, and already this season are nought from two in escapes from that uncomfortable position beneath the pump.
"This is where the magic has to materialise. Forget the easy coaching bits about improving skills and working out tactics.
"The best coaches are able to teach players how to perform under the intense pressure of the critical moment.
"There can be 10 or more critical moments in a game, and they can occur in the second minute or the 78th. The five-star coaches have their players primed to react as they need to, when they need to.
"That part of Deans' coaching has, to this point, failed. "
Slack's comments were seized on today by The Australian newspaper, under the heading "Deans doctrine coming up short".
In the Sydney Morning Herald, rugby writer Greg Growden preferred to apply the heat to the Wallabies players, and offered a novel solution.
Rather than collect their reported $A11,500 ($NZ14,100) per test, regardless of the result, he suggested $A15,000 for a win and $A5000 for a loss.
"I can guarantee you the standard of performance would improve," he wrote.
Growden said Deans, coming from the intensely competitive environment at the Crusaders, was now faced with dealing with a softer atmosphere where some Wallabies were in "cruise mode" due to a lack of player depth.