GOOD full-backs are worth their weight in gold. It is one of the most difficult positions to play and the fellows who hold down the position rarely enjoy the responsibility. One of the best of all time was my old teammate Geoff Southby. Geoff dominated at full-back for more than a decade, but each summer got into the coach's ear about being played up forward.

The AFL full-back of the century, Stephen Silvagni, was also keen to get out. "SOS" delighted in the freedom of the forward line, and actually kicked more than 200 career goals, but it was his ability to control the likes of Wayne Carey, "Plugger" Lockett and Jason Dunstall that made him so valuable to the Blues.

I think today's full-backs do it really hard. A few years ago, "flooding" tactics helped the defenders as lots of members back blocked the full-forward's leading options and caused the ball to come in slow and wide.

Now there is less flooding, so the ball is directed to the forwards in a quicker, more direct fashion. And the full-back is now penalised if he sweeps the arms or makes contact with the head, neck or back, when he tries to spoil. And heaven forbid if he hangs on to a jumper. Yesteryear's full-backs would have given away 10 free kicks a game by today's standards.

So to spoil without infringing has become a real skill. Probably the best example of this was seen on Friday when St Kilda's Max Hudghton repeatedly got his fist on the footy to spoil Matthew Lloyd. The Essendon skipper took only the one mark and was held goalless. Hudghton didn't concede a free kick as his well-timed spoils meant that fist smashed footy, not body or skull.

On Saturday at Geelong, it was a delight to see two veteran full-backs in action. In Matthew Scarlett's previous seven games, he had conceded one goal a game and had averaged 20 disposals himself. Incredible figures. Not only that, he is continually looking to place the ball in the central corridor when he rebounds. He did it again against the Swans. He kept his opponent Michael O'Loughlin goalless and launched half a dozen attacks that resulted in goals. At the other end of the ground, Leo Barry had his hands full with Tom Hawkins. The Geelong teenager is 11 years younger and 13 kilograms heavier. Leo couldn't budge the boy in marking contests, but realised he could outrun the kid and thrilled us with some zigzagging runs out of defence.

And then on Saturday night at the Gabba, we saw two hot full-forwards stress out their immediate opponents. "Buddy" Franklin had 14 scoring shots for his Hawks. Brisbane Lion Daniel Merrett, the most prolific spoiler of all the full-backs, couldn't catch him, nor reach the ball when Franklin stood upright with arms outstretched. That performance alone is a good reason why no one will want to be on him over the next decade.

But at the other end of the ground, the Hawks had problems. The undersized Campbell Brown had a bag of goals backed against him by the taller heavier Daniel Bradshaw. The experiment of playing Brown as a key defender has been a success, but maybe opposition clubs are realising that if you drag him back towards goal, his mistakes against bigger opponents can be fully exploited. Maybe time to freshen up last year's All-Australian by playing him on smaller opponents.

But of all the full-backs, the one who had the most confusing role of round five was the Bulldogs' Brian Lake. His opponent was Matthew Richardson, who spent most of his time on the wing. Lake was instructed to hold his position in the back line, so he virtually was free.

With the Bulldogs two goals down with two minutes to play, Lake showed pleasing initiative. He left his post in defence and pushed to the Bulldogs' half-forward line, where he took two marks that resulted in goals and ultimately a drawn game.

Lake would have got out of the game something that full-backs rarely do. He would have got some fun and enjoyment out of kicking and creating goals. Usually, the best a full-back can hope for is satisfaction. The satisfaction that comes from limiting a star player to an ordinary game.