Yeah there is one way to protect your card, I take mine out (it doesn't need to be in all the time) We've had 2 replacments already the staff at sky have been very understanding about it.
I just put it in when I first change the channel and take it out about 5 mins later, it works most of the time without a card anyway so it's not always necessary.
That or you could do what they used to do in days of old and cut the offenders hands off.... extreme I know but will save you lots of trouble in future. I keep threatening ds with this, he thinks it's funny but one day .......