I don't know that there's an easy way to guard against the threat, short of holing up in a bunker or going out of town to visit family in the next state.
But, and I'm sure this is being done since LAPD isn't exactly known for standing idly by, we need to put this idiot on the defensive. Send teams of officers out to actively hunt for him. Start putting pressure on him by any means, and I'm sure the press releases are only one tool being used. Plaster his face up on every TV screen and internet news site out there. Put his name out on the radio, and start offering a decent reward for someone who turns him in.
In short, make it hard for him to hide, or to get support from others. As I said, I'm sure LAPD has already implemented this strategy - and we don't need to know what they're doing. But, the best way to defend against a guy like this, is to put him on the defensive. Actively hunt this SOB down, and put him in the ground as you would a rabid dog.
Good luck, and may God be watching over our brethren and their families - especially now.