Without boring you with details, in my world, a government is try to protect a package from ninjas crossing over from another world.
The technology in this government's world is about the same as our own. The ninjas' technological level, by contrast, is about the same as Japan in the Colonial age (late 19th C).
Ninja magical powers include:
invisibility: can be seen on cameras or with heat vision goggles
mind reading and control: limited to one or two minds at a time
create illusion: also limited to 1 or 2 minds
Ninja weaponry is also magical, such that even a single scrape will kill.
Ninjas can cross over at any place in our world.
The portals that the ninjas make range from small (can fit two or three people) to large (can fit around 10).
Portals can be made to prevent this-worldly objects from crossing over to the other.
Objects that pass through portals must go all the way through. No just sticking your hand out and snatching the case through without leaving the safety of the other side. Similarly, if people on the other side want to bring something to their side they have to actually go through the portal and get it: they can't just open a portal to where the object is in our world.
The Government Agents
To combat these ninjas, the government has access to a new technology that allows agents to see and track portals to the other world once they open. Agents cannot cross into the other world. The ninjas do not know about this technology.
The package is small enough fit into a briefcase.
Neither the ninjas nor the government are willing to destroy it.
The package is a very powerful magical object brought over from the other side. The government doesn't know what it does or why the ninjas want it, but they suspect it is the key to understanding how the ninjas' magic works.
It is unlikely that the government will be able to get their hands on another object from the other side, so this could be their only chance.
The government wants or needs continuous access to the package. Thus they cannot simply seal it in concrete or the like. That is, whatever vault or container they put it in must have an openable door of some kind.
The ninjas have a way of tracking the object in this world, but it takes a long time to narrow it down to a specific location. Thus, simply hiding the object isn't an option, but it will buy some time to prepare.
Knowing that the ninjas will come for the package eventually, what can the government do to protect it?
Note: it is probably that the ninjas will try multiple times. Whatever defenses are chosen must be flexible enough to withstand multiple attacks.