Build camps on islands to house all illegal migrants and asylum seekers until their cases are processed and they are deported or allowed entry. Separate by gender, men on one island and women on another island. This is for the protection of the women and children and also to keep the number of illegals from growing while their claims are being processed, and to keep new “citizens” from being born in the camps.
If a migrant needs to be deported and their country of origin cannot be determined or refuses to take them back, they will be kept in the camp until a country can be found to take them, which could be a very long time.
In the meantime, they cannot be allowed to intermingle among the general population awaiting their court date, which is why they must be kept on islands, where there is no chance that they will end up on the mainland.