[jwilliams]

In the past I've requested explicit opt-in and out.

Usually there is a blanket IP clause, but if I say "I'm going to work on ABC in my spare time" - and we all agree this isn't core the business - then it's added as a schedule exclusion.

You need to be specific, but it works just fine if all the parties are operating in good faith (which you'd hope with a good employee relationship).