Typically we will work with the municipality to gauge the needs for homeless overnights before they take civic action like citations and arrests. This way we insure that there will be enough space.
There will always be some that reject a shelter and usually a time window is worked out where a homeless person has to be off the property if they only want to sleep.
There is a balance that can be struck between the needs of the homeless and the publics desire for safe and clean parks.
I am not familiar with the Idaho situation directly, but legal action usually occurs when compromises cant be reached.