Can anyone recommend a method whereby malformed queries executed against a PSQL table without using an index can be prevented? Execution of these queries causes serious slow downs on our server.

For example, a user writes a query without using an index. Or, uses a 'like %' in a query searching for text in a field without indexing.

Tasering the users hasn't worked so I'd like to cut em off at the source.

Matthew.

About the only way you're going to prevent users from writing malformed queries is to prevent them from running any query except approved queries.
Now, if they are using the same query often and it doesn't have an index to use, I would suggest creating the index.