Nice work on crafting "fenced off!" You can use it and other fortifications you craft in your strongholds (SHs) to upgrade the defense. SHs can range from Level 1 to Level 3, with Level 3 being the highest and best.
Fortifications will help protect your survivors (NPCs) inside that particular SH from attacks from other players. No SH is invisible, yet fenced off and other fortifications will make it a little more difficult for other players to take it over.
Putting fortifications and traps in a cluster of SHs can also begin to attract in-game survivors every ten days. Make a cluster of 3-5 SHs, make them all level 3 SHs, each with 3 traps. Put 150 days of supplies in one along with a current survivor (NPC) if you have one, and 100 days of supplies in the other SHs (without a survivor inside) in the cluster. After about three weeks, you'll have a survivor show up at you SH with the 150 days of supplies. You can choose to have them join you or you can tell them to move on. I recommend having every possible survivor (NPC) join you. It will make fighting Zed much easier. Every ten days after that, you should receive another one. Hope that helps. If you have any other questions, download the Palringo messenger, search for the group Freedom Outpost. Join that group, as it is an active group to find info and tips about SZ.