Add command /lockmob to "claim" a mob. This would make the mob invincible and immobile until unlocked by a subsequent /lockmob command from the same player (or staff). This is to parallel the existing /lockstand command. To prevent exploitation and hinder mob-spam (like people do with chickens), I believe this should only be available to mobs which have a name (via nametag). It would still be possible to create a number of locked mobs inside another player's build, but requiring names would make it more work and much more expensive. Mobs should still be affected by right-clicking, to trade with a Villager or feed other mobs. This was suggested as a server-feature by Anna_28 in game at 2022-02-06T03:27 during a conversation with abamacus and RebelCommander7, who were arguing that a mob can be part of a build, and therefore killing them could actually be grief. Since armor stands have exactly the same problem, this solution seems ideal.