My solution two years ago was to establish an indoor shack in the spare room and run a couple of Heliax coax cables from a patching frame in the outside ( garage) shack, under the lawn and then along the fence line to the side of the house. As well as the two main coax lines I have a six wire screened control cable between the garage and indoor shack. I also have a third coax for HF that shares some of the common route but goes to the bottom of the garden. All cables enter the house through Huber Suhners lightning arresters.
With these few connections full remote operation is a bit of a challenge. I decided ( for now) against using e.g. Remote Rig or similar due to cost.
Last winter I ran my K3 as the 144MHz IF over one of the coax cables, with the various microwave transverters in the outside shack connected to the IF as required. The problem with this arrangement is that the losses in the long, concatenated, coaxial cables between the mast mounted transverters for several of the bands and the indoors IF were just too high and tended to radiate enough to be heard locally on 2m!
The solution this winter is to locate an Anglian 28/144MHz transverter in the outside shack and feed 28MHz IF over the coax. Yes, there is still a danger of egress and ingress at these frequencies, but the coax is pretty good at 10m.
Since the K3 and the Anglian 28MHz IF are separate ( transmit and receive are independent) and I didn't want to use up both of the coax cables between the two shacks, I intend to use a couple of 3dB splitter/combiners rather than relays in order to separate the transmit and receive paths. Tests with two MiniCircuits splitters and a 6dB attenuator have shown that the idea works well.
The second coax cable will be used for a second system, with another rig.
PTT is activated over one of the screened cables and when the transverter is switched to transmit the Anglian +12V on transmit signal is connected to another control cable wire ( through a current limiting resistor) to light an LED in the indoor shack as confirmation that the transverter has switched.
I also use a Bird sensor on the 2m transmit output in the outdoor shack and feed the sensor output back over a third control cable wire to the meter ( still in the Bird housing) in the indoor shack in order to check that there is actually transmit output.