Just designate one of the parishioners to guard the entrance with a modern sporting rifle and a 30 round mag. That person /persons can rotate each Sunday. Like a duty roster if you will. I’m sure there would be an ample number of volunteers each Sunday.
And full SWAT gear with a Cross patch on the shoulder.
Even the ancient Temple at Jerusalem had an armory and guards. Why should churches today not have something equivalent?
Of course, it will give the naysayers an excuse to criticize churches for being “like mosques”.