I didn't want to side track the magical focus thread any more...

I thought if you didn't agree to partake in certamen you automatically loose and are obligated to provide what ever the wager...hence you can be forced into certamen.

How would you get around this?

You are still choosing to participate here: you are choosing not to accept the social stigma of forfieture.

Also, certamen basically it isn't for wagers. Certamen is a form of legally-recognised duelling meant to act as an intermediary between verbal conflict and Wizards War. It -is- used as a sport by Tremere magi, and some others, but its function isn't for gambling.

Finally, as an out of game reason, if you allow a PC to take this they gain no advantage, they just can't participate in certamen, and thus lose the stopgap between words and War. That's not worth as much as say "Greater Immunity: Drowning".