Disguise is the best defence I think. Works for sheds, not for domes.
Quality door locks, and strong door. A door that happens to be quite sticky/jammed helps too (confuses legitimate people who try to open the obs, so why not crooks
).
Off-site data backup is a must, easily done to the house and vice-versa, with the network cable hidden of course.
In addition to data, if you house is nearby (say < 100m) you can have a 2-4 camera security set recording the area and having the data stored "offsite" in the house, with UPS backup. Fairly reasonable price these days. Most of those recorders will easily fit in a tucked away place in the house, hidden from being stolen themselves, and only needing a network cable to be able to maintain & monitor them from a PC.
Good locks on the roof is an obvious one I guess, so the roof can't be opened easier than the door.