What pattern to check on an SQL query for possible injection?

I want to detect possible SQL injection atack by checking the SQL query. I am using PDO and prepared statement, so hopefully I am not in the danger of getting attacked by someone. However, what I want to detect is the possibility of input/resulting query string that may become a dangerous query. For example, my app--properly--will never generate "1=1" query, so I may check the generated query string for that, and flag the user/IP producing that query. Same thing with "drop table", but maybe I can check only by looping the input array; or maybe I should just check to the generated query all over again. I am using MySQL, but pattern for other drivers are also appreciated.

I have read RegEx to Detect SQL Injection and some of the comments are heading in this direction. To my help, I'm developing for users that rarely use English as input, so a simple /drop/ match on the query may be enough to log the user/query for further inspection. Some of the pattern I found while researching SQL injection are:

• semicolon in the middle of sentence -- although this may be common
• double dash/pound sign for commenting the rest of the query
• using quote in the beginning & ending of value
• using hex (my target users have small to low chance for inputting 0x in their form)
• declare/exec/drop/1=1 (my app should not generate these values)
• html tag (low probability coming from intended user/use case)
• etc.

All of the above are easier to detect by looping the input values before the query string is generated because they haven't been escaped. But how much did I miss? (a lot, I guess) Any other obscure pattern I should check? What about checking the generated query? Any pattern that may emerge?

tl;dr: What pattern to match an SQL query (MySQL) to check for possible injection? I am using PDO, so the check is for logging/alert purposes.