Wasn't "3-tier architecture" suppose to
be the solution to this sort of thing?

Another trade-off you make when you validate
the heck out of everything is that you lose
maintainability.
It would be nice for people who will maintain
your code that you do your validation in "one place"
"One place" meaning that your validation code be
easy to find and maintain.


--
Write all your code as if all your operations
and maintenance programmers are axe murders that
know your address!