It's timely you should ask. That question has come up many times over the last few years with several creative ways to solve it. Everything from multiple recorders, hidden recorders, dummy recorders, shared link with neighbor and more.
One of my dealers resolved this with a single FX-PRO camera located in the area of the DVR/NVR. It has backup battery and local storage as well as cloud for events.
It won't save all the other video but it will at least get an image of who took the DVR! It wasn't my idea, but I'll share it anyway.
There are other products that would do the same thing I'm sure.
A few thoughts...
In similar situation in the past I've advised people that if they have an older DVR (or even tape!) style system to leave the old recorder in place and powered up. It makes a good decoy, and is probably more what the average smash-n-grab thief would be looking for.
In a small system like what you describe (4-8 cameras?) a small PC can typically act as a sufficient NVR, and it probably wouldn't attract much attention (thief is probably looking for something with a bunch of cables going to it). You may be better served leaving the PC/recorder out in the open, like on a managers desk, rather than try to lock it down and make it seem "important". The downside of this is that if the employees know this PC is the recorder, and are shady, it's easier for them to mess with it.
If there is a very big risk, with IP cameras you can often do multiple streams, so you can have redundant recorders easily (other than of course the added cost). With cheap NVR's, you could have one in the open, and another hidden in a ceiling, or hidden in something like a circuit breaker box that isn't for power, but just to house the DVR. If you do something like this, put 4 or 5 coats of paint over the box to make it "blend in" and not seem like a new/shiny thing on the wall.
Setup a gmail account for free. Use an NVR/cameras that can email on motion, set the email alerts for only after hours and go to the gmail account. If someone breaks in and steals the recorder you *should* have at least a handful of emails that has images of the perp. Kind of like a cheap/free VSaaS.
Use cameras with SD card recording in addition to the NVR, they'd have to steal the recorder AND the cameras in that case, which I think would be EXTREMELY rare.
And of course you can bolt a DVR lock box to a sturdy point up high to make it hopefully take longer to get at the recorder than the thief wants to spend.
In addition to all the excellent ideas so far, you could use external storage (iSCSI, etc.) stashed away while leaving the recorder somewhat easier to find (if not right in plain sight)... then if they take the recorder, the video itself is still safely kept on site.
Some cameras can also record directly to network storage as well as their onboard storage, and they could take advantage of the same unit - for example, a consumer/SOHO RAID like QNAP, Netgear, or Synology can have both iSCSI and standard SMB volumes to support both in one place.
Some of these RAID units also have their own NVR functionality that could work as a backup, even if they only record a substream.