Chava, I don't know if you recall the church fires that were going on a couple of years back in Alabama (mostly rural and many within walking distance of homes) - but that was another call for increased security in our congregation, as we have a Torah, and it was being stored in an Ark, but not otherwise protected.
A member had an ingenious idea to modify a fire-safe so that it would comply for the needs of our scroll, protect it when not in use, and yet have the ner-tamid .. very interesting complication we had, and no one had ever encountered it before.
On top, we had to make some structural changes to the building to bring it up to code as it used to be a home, and was no longer. It had to meet some new fire codes (Doors had to open a certain way, no more than X amount of seats, etc).
Prior to that, around 9/11, we had some major draw to security, and started implementing some plans. Closer to '04 or '05, we had a mosque open not too far from us, and between the craziness that broke out with that, we had some really ignorant "Good ol' boys" getting itchy and territorial, so we increased security again, and those who had permits to conceal-carry had dedicated to do so when it came to meetings and also coming together for Shabbat.
We also contacted the security firm that looked over our congregation, and the local PD. They increased their "drive-by" on our road, and often would come up and check things out if there seemed to be a car parked at an odd time. I remember one time I was setting up for something, and had dedicated to come between my work to home hours (as rush hour at that time of year going home was horrible either way I went home, and the Synagogue was along one of the routes) -- an officer pulled in the driveway within 10 minutes of me pulling in.
You shoulda seen my face.. LOL! I was pleasantly surprised, and we got to chat for a minute when I explained who I was, why I was there and that all was well. I did let the elders know that we definitely were being checked up on.
When I had visited our local Conservative shul, the police stand at all entrances and also drive by (it's not too far from the inner city, but it's closer to the nice area of the city) - the security was rather good, but not as good as what I've seen at some churches (consealed-carry ushers, organized parking/ persons looking out at the entrances/exits of the parking lot and around the building, individuals keeping the children's areas safe and looked over, closed doors during services with individuals "casing" the building (services being broadcast on speakers so they don't miss out) and heavy emphasis on meeting/greeting new attendees)...
I think we could do more for our security, but I haven't been other than to visit the few times my morning sickness cooperated, and what I did see was much better than when I last attended my home congregation. I think some CCTV/cameras might benefit as well as reflective mirrors in the parking area, and someone keeping an eye on the parking area during services (erev shabbat for instance) might be better ... other than that, there isn't much they really can do, short of splitting down to splinter groups meeting in homes and agreeing to meet only at certain times of the month together. KWIM?