Actually I found a way to lock additional home gates and community lots (that your sim owns) gates.
1. Go into the build mode (or buy mode).
2. Hold down Shift+Ctrl.
3. Cursor over and click on the gate you want to lock. It should come up with a list that says: Lock, Clone, Add the ability to add triggers and activated behaviors, and Thumbnail camera...
4. Click the Lock option (duh) and it should automatically lock for sims and pets.
It works but the only problem with it is that it locks out your sims and your pets and then when you want anyone to go through you have to go back to build mode and unlock it. But, it doesn't use any mods or cheats for all the people who aren't comfortable installing mods.
Hope this helped and happy simming!