Do you want to temporarily feature something that would change the setting drastically if it became an ongoing feature? The Agents Of S.H.I.E.L.D. episode T.A.H.I.T.I. addresses this issue in a couple of useful ways.
Cut for spoilers:
Our heroes visit a medical facility with the capability to raise the dead.
1: It’s secret. Obvious place to start.
2: It’s well defended. Also sensible.
3: It’s of interest to the enemy as well. Getting their hands on it would be disastrous.
4: It’s distinctly limited. The miracle drug has a unique source.
5: It’s destroyed at the end. The agents don’t even have to be the ones to do it. They get just enough time to explore and get out before it all goes up.
Any two or three of these after the first should cover you. Just one could be subject to the PCs taking the prize, luring the enemy with it, making more, stopping it being destroyed, and so on. And be sure to establish several in advance, so you don’t unfairly start adding reasons to remove it as the PCs disable them. Play fair.