If I understand what you are asking for, I do it all the time.
What I have done is created a "Clients" group. I set the access control for this group to "owner view only." Users can't see the group.
Then within this group, I create galleries for each project. Generally, I don't password protect them -- I set the access control to "public - open to all." This way, I just give the URL to the client, and then can get to it directly without using a password, but it's pretty much impossible to browse to. Works GREAT!
For projects where for whatever reason, the client is concerned about privacy, I take the additional step of adding a password.
Using this simple approach, I have hundreds of galleries that are not visible to the general public, but my clients, with the proper URL, can go directly to them.