You should have at least put a note that stating "Due to security issues with the block chain for the coin you are transferring we have had to increase processing to 200 confirmations. This could delay the availability of your coin for up to 24 hours. Please note this prior to confirming that you are transferring these coins to your wallet here on Cryptopia."
That is a very good suggestion.
Other solution as you stated in a previous post - just don't list insecure coins and get rid of any coins that aren't secure and no one would have lost money on a 51% attack.
And this one is a pretty much nonsensical suggestion. I suppose the coin you were trying to deposit, will be one of those to be delisted. But as you are making this suggestion, I assume you don't care, because you don't belong to the community of those coins, and just want to earn few fast bucks on arbitrage. This is a kind of solution which will make couple of traders happy, but a bunch of coin communities unhappy. Care to think a bit before posting.