Should managers carry a sack-by date?

IF necessity is the mother of invention, there are a few football managers who could do with reinventing themselves.

Jose Mourinho and Arsene Wenger will go down as two of the greatest bosses in the history of the game, but are in severe danger of tarnishing their respective legacies.

Once the masters of innovation, they were new brooms who swept all before them. Such was their impact on English football that even Alex Ferguson had to bow to their superiority for several seasons.

But where the great sage of Old Trafford adapted and rebuilt, the Special One and the Myopic One have stuck stubbornly to the modi operandi that won them trophies in their enlightened prime.

Wenger got Tony Adams to eat pasta instead of sup pints (!), changed one-nil merchants to several-nil Invincibles and turned Thierry Henry from a forlorn Juventus winger to the greatest striker in Arsenal history.

He was hailed as a revolutionary before being overhauled by Mourinho's first coming at Chelsea.

The Portuguese was fortunate to benefit from burgeoning existing talents and Roman Abramovich's billions, but brought great charisma, confidence and tactical wizardry as well as being a master motivator.

It is both sad and sobering therefore to see them now, many troubled years and a thousand disputed penalties later, as two grumpy old men.

Their current teams aren't half bad, but the point is – and this is surely eating away at them – they have been overtaken. Left behind on the hardest of shoulders. Yesterday's champions disappearing specks in the wing mirrors of younger men with more vibrancy and newer methods. And all they can do is moan.

Between them, a broad swath of mankind has felt the serrated edge of their tongues, but above all it has been referees who have borne the brunt: they are never wrong.

They are not alone, of course, just the two most notable of the genre. The pundits' sofas are filled by failed managers or those who have succeeded once but lost their mojo. The casualties are several rows deep which suggests that, like players, a manager may have a limited lifespan.

Ferguson is Exhibit A, B and C for enduring effectiveness, but for every Sir Alex there are a dozen Alan Pardews and even more Alan Curbishleys – forgotten.

Pards has yet to win in nine games at West Brom and can no longer even rely on a decent honeymoon. His stay on the carousel of failed British bosses who are perceived as safe pairs of hands must be running out.

Mark Hughes, David Moyes and Tony Pulis are others who get jobs but never win anything. And it's significant that the most successful of this breed, Sam Allardyce, only does salvage operations and once the job is done, doesn't stick around.

This is not an argument against longevity but complacency: tried and trusted can become a broken record but age does not mean failure. Bayern are responding to 72-year-old Jupp Heynckes while Guy Roux always managed to keep things fresh at Auxerre during a remarkable 44 years.

Roy Hodgson, 70, has taken Crystal Palace up the table after a negative stint with England. And he's done it by switching to attack which he wasn't afraid to do even against Man City.

Conversely, Wenger has dug his heels in at Arsenal even though his career is one of two glaringly different halves. Without a trophy apart from three FA Cups since 2004, his teams still try to walk the ball into the net and are dodgy at the back.

He's so powerful at Arsenal, the club are afraid to sack him while he's hanging on, afraid of retirement. Well, he always did have trouble seeing things he did not like.

Similarly, Mourinho's star has waned. He was probably at his peak when he won the Champions League with Inter by parking the bus in 2010, he has since secured domestic titles with Real and Chelsea but both of those stints ended in dressing room implosion.

So much so that Man United fans were split over his appointment 18 months ago and now, despite being second in the league, the majority are sick of his antics and negativity.

He only seems to know one way – a big, bulldozing centre-forward and a double-decker bus behind.

Now he's dangerously close to biting the hand that feeds him by slamming the transfer budget as well as club legends. No wonder rumours are rife that he'll leave for PSG in the summer.

It is all the more surprising as he knew what he had to do. He has changed but not in the way fans wanted. Once a big brother to John Terry, Petr Cech, Frank Lampard and Didier Drogba at Chelsea, he's now like a cruel step-father to his current crop.

At Arsenal, the fans are similarly divided but Wenger's frugality is lauded by the board. But that he should equal Fergie's record of 810 Premier League games raging at the referee was an appropriate testament to what he has become.

He and Mourinho are mortal enemies yet united by the need to prove they know best. Once players wanted to play for them but now it's Pep Guardiola and Jurgen Klopp whom they see as mentors.

Mourinho is no longer special while that banner claiming 'Arsene Knows' was taken down years ago.

Another thing they have in common and what is in stark contrast to Fergie is backroom staff.

Mourinho has the same Rui Faria-led team throughout while Wenger has had first Pat Rice and then Steve Bould. Fergie had a constant change of input from his many assistants.

At a time when expiry dates are being relaxed in the food industry, the mischievous thought occurs that they should be introduced in football: sack-by dates for managers. Like players, there are some who lose their freshness and become unpalatable shadows of their former selves.