DROP TABLE permissions default to the table owner, and are not transferable. However, members of the sysadmin fixed server role or the db_owner and db_dlladmin fixed database roles can drop any object by specifying the owner in the DROP TABLE statement.
If even the above should not be able to delete a table, make the database as read only
EXEC sp_dboption 'databse_name', 'read only', 'TRUE'
Remove all the users accounts from db_ddladmin role. Even this can’t stop members of sysadmin fixes server role to drop the table.
