THE decision to exhume the career of Fraser Gehrig was an easy one for St Kilda, because it was the G-Train who did the spade work.

He wanted back, and the club were more than happy to rescind his retirement.

Gehrig cost the Saints only pick 57, a spot on the list and fewer dollars than he earned in 2006 and 2007. Where was the downside?

He would be a handy foil for Nick Riewoldt and Justin Koschitzke, insurance in the event that the accident-prone Kosi ran into a ladder.

Even on Gehrig's increasing bad- hair days he would take a good defender. Accepting a 32-year-old, dual Coleman medallist wasn't a tough call in November. But today's selection decision on Gehrig was - and is - a very daunting choice for Ross Lyon and his match committee, for "the G'" isn't such a force now.

Gehrig's form line over the past two-and-a- bit seasons has headed slowly but inexorably for the Mexican border. While he remains capable of tossing rag-doll defenders around and kicking a bag, some of the better key defenders have his measure.

Exhibit A for the prosecution is Geelong's Matthew Scarlett, who, admittedly, removes the trousers of nearly every key forward in the competition.

Last weekend, Scarlett didn't simply halt the G-Train, he ran off him to the tune of 24 disposals.

Scarlett butchers any forward he knows he can run away from, and Gehrig isn't built for marathons.

Since 2006, Gehrig has averaged fewer than two goals a game against the elite full-backs - Scarlett, Adelaide's Ben Rutten and West Coast's Darren Glass. In his 2003-2005 prime, the G-Train could beat the best, Scarlett included.

This year, he's booted seven goals in three matches - four of them against Carlton. He did not play in round one, when the Saints pipped Sydney.

If Gehrig will still have good games against certain teams and opponents, the corollary is that the Saints now have to consider whether he's suited to other teams and defenders, and Gehrig must accept that there are games he should sit out.

Gehrig is said to be a bright bloke with real footy nous and one assumes he and Lyon have already had that conversation. He would know that, like Robert Harvey, he's not expected to play 22 games plus finals this year, and that the Saints plan to rest him on occasion.

The tricky part is when to hold and when to fold the Gehrig card. It won't always be clear- cut.

Tomorrow night's game, at first glance, appears to be one of those grey areas with strong arguments both ways.

The case against Gehrig's selection this week is that Essendon has two quick, agile tall defenders (Dustin Fletcher and Paddy Ryder), that the Dons are an adept counter-attacking team and that St Kilda can ill-afford a three-talls forward structure against a team with serious leg speed.

Further, in Mal Michael, Gehrig has a prospective opponent who matches him in body-on-body duels and did pretty well on Gehrig even when the Saint was winning Coleman medals.

Or, if Matthew Knights feels adventurous, Essendon might send Michael to Koschitzke and punt on Fletcher and/or Ryder running off Gehrig.

The argument for Fraser's selection this week would be that he's needed to ensure that Essendon's tall defenders are made accountable to their opponents. Fletcher is expert at intercepting opposition leads, getting loose and launching counter-attacks.

The Essendon veteran can play on smalls - he could man Stephen Milne, if required - and teams that don't make him accountable to a vaguely threatening opponent (one who has to present and actually get the ball) tend to get minced.

Assuming St Kilda hasn't picked its team yet, the Gehrig decision promises to occupy a fair portion of the Saints' selection meeting today. And the quandary will be revisited throughout the season, perhaps once every three or four weeks.

The Saints aren't the only club with an ageing key-forward conundrum.

Collingwood would be facing similar questions about Anthony Rocca - another gorilla the opposition can exploit on the rebound - if not for the fact that the Magpies, sans Sean Rusling, are employing a two-talls forward structure.

Melbourne also would be confronting a David Neitz migraine except that it has cluster head aches everywhere.

Rocca, too, beats up on certain teams, and is apt to be smashed by Scarlett and Rutten.

Rocca's advantage, relative to Gehrig, is that he provides a superior aerial contest and better spillage for smalls. For Collingwood, the question is less pressing.

Fraser Gehrig was for ever considered an enigma. Now, in the dusk of his remarkable career, he has become a riddle.