Maybe this is a stupid question, because very likely it is possible for advanced learners to distuiguish this. However, in the present tense ...でする (particle で) and ...です (copula) are distinct, while in the past tense they sound the same.
My current way to cope with this problem is to search in e.g. Google for expressions using the present tense, i.e. either です or で+する and compairing the number of found pages.
Example phrase: 思い出でした
Google hits for
思い出でする: 22 思い出です: 2.7 million
Clearly, copula wins over the other "possibility". This is rather awkward. Especially if there are terms that are less frequently used so Google returns either way few pages. Is there an easier way I am not seeing?