You have two choices, depending on how many clients you have and whether you want one client to have more than one login account for different people.
The simplest approach would be to create a role called External Clients and give that role permission to view their own catalogs only. That basically means unchecking ALL the permission options for that role. You can include the “Edit own catalogs” permission if you want but make sure you uncheck the “Read other users’ catalogs” option. Then, either open the catalog from CatDV Pro, use Edit > Catalog Details from the menu, or right click on a catalog in the catalog tree and choose Catalog Info, to bring up the catalog details panel where you can view the group and user the catalog belongs to. If you’re an administrator you can change the owner user to be that of the appropriate client. (Alternatively, if you’re not the administrator, just make sure you log on as the relevant client when you first publish the catalog to the server.)
A more complicated solution but which potentially gives you more control is to create a separate production group for each client. Each external user will belong to just one production group and can see all catalogs that belong to that group, but if you have a lot of clients there will be more work involved in creating all the groups and roles. Obviously your in-house staff will need access to multiple production groups, unless they work exclusively for one client, so you can either give them access to the wild card “system” group or explicitly give their role access to all the groups they work on.