The secret to Westboro Baptist Church is that the entire congregation, which is mostly family and extended family, are all legal professionals. Most of them are trial lawyers like their departed father.
Believe it or not Fred Phelps was an astoundingly good civil rights attorney in his heyday.
Turns out his heart wasn't in it and he was extremely cynical about it but he won case after high profile case and got a lot of money awarded to his clients.
And therein lies the secret, the family secret.

Westboro's "parishioners" never protest ANYTHING unless potential deep pockets are involved.
Any attempt on the part of a city, state, municipality or any other public or private entity that has deep pockets to block them, accost them, confront them in any way that involves any kind of threat or denial of access results in a lawsuit filed by them that charges that said entity denied them their "civil rights", and the name of the game in Westboro's wheelhouse is to settle before trial, which is what almost always happens.
They are paid to go away, or make the case go away.

And the secret to preventing them from protesting is simple, take away the deep pockets.
If they don't think there is any chance of making any money, they will not show up.

The Phelps Family has managed to refine civil rights litigation into a fine art.
There is nothing remotely religious about it, it's all about the ducats.

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