Hi Wee Edie
TBH, my external backup drives (2 x 1Tb USB drives) are never physically connected to the PC unless I'm doing a backup. In actual fact they aren't even kept in the same room as the PC or our home server. I backup deltas every weekend via FreeFileSync and it only takes a couple of mins to grab the relevant drive and plug it in.
I suppose you could keep the drive physically plugged in and connect/disconnect via Task Scheduler or similar but these damned malware authors seem to be getting smarter and smarter. That being the case, I'll stick to physical separation of drives to keep the backups safe (assuming, of course, that I don't manage to infect my PC before connecting a backup drive :-) )