Guid like strings in SQL

we were having an issue that there was a table that had all string values, guids and non guids, and a join on a guid table was failing so we did this

      select * into #blah

  from

  blah WITH (NOLOCK)

       where string_val LIKE REPLACE('00000000-0000-0000-0000-000000000000', '0', '[0-9a-fA-F]')