Limiting people to add time entries

Hi to all,

the title is probably misleading, anyway, I encountered the following issue:

in order to track time we have some "general activities" which are always open in order to have people track time. This is due to the fact that part of our time does not work on a "planned tasks" basis and also for the rest of the team to register unplanned activities that are listed as support to other departments.

My issue is that one of the designers (whose work falls in the second category) out some time entries in one of the general activities of the first kind, which is not assigned to him but in the same space.

How can I avoid this? Should I separate the spaces and limit access in order to avoid this occurrence? Is there a way to avoid such occurence without having to create new spaces?

Thanks.