The point is: adding that “feature” to every app doesn’t scale. Other apps implementing it nonetheless doesn’t mean it is a good feature. Here is another solution which might fit your needs better since it keeps your server hidden from the internet:
Give your server a DNS name which is only resolvable in your home network. Then if you’re on the go, the domain will not resolve and there is no connection to a wrong server.
Log-term syncing with davdroid
I prefer to have all my calendar entries (last 10 years and more) on my mobile device. If I clear the day parameter for past entries in the davdroid settings it works and I get all my entries from owncloud after synchronizing. But if I change this parameter back to e.g. 90 days (for reducing sync time) my entries oder than 90 days disappear after syncing. Is this a wanted behaviour? Is there a possibility to keep the old entries (difference between long-term and normal sync)?
Yes, this is the wanted behaviour and no, there is no option for that.