PHP SQL Injection Prevention Technique

[brendyboy]

I'm starting to think about protecting my inputs from SQL injection. I've read about PDO and mysqli and will be using those techniques. While I was researching protection against SQL injection, I had a thought about a technique. Whenever I have an input from a user, I could scan the input string and search for occurrences of "'" or "DROP" and if the string contains those characters, then I could just not proceed. Would this technique prevent a lot of SQL injection?Thanks for your help.