Form validation on checkout page

I need to add form validation on the checkout page to stop hack attempts.
We’ve had a number of orders where the customer name has been replaced with script code.
Fortunately, this hasn’t done any harm, but I would like to add validation to stop code being inserted.
There is a full list of Magento validation options including a tutorial (but I’m still not sure how to implement it) in the link below, but I don’t know how to add it to the checkout page.
Can anyone help?
Many Thanks
Andy
Full list of Magento validation options