What should be used as a catalog category code?

Summary:

What you would you recommend to use as a catalog category code if multiple catalogs are used and each having up to few thousands categories?

Content (required):

We faced this issue after customer requested to replace existing catalog with a new one. We used category description as a category code. Firstly, it might be long and containing different characters. Secondly, few category codes happened to be same as in other catalog. How to validate it in advance? Any "user friendly" way?

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