Warning when double booking trainers (extra trainers on courses, events & booked assets)

Currently we receive a warning when a trainer is double booked on two courses as the primary trainer but we do not receive any warning when a trainer is double booked in any of the following circumstances; 

- As an extra/secondary trainer on a course 
- For an event
- As a booked asset 

Having a warning that a trainer is already booked in theses circumstances would be very useful for us as it would significantly reduce the risk of a trainer being double booked by accident. 

Thanks,
Tahni