I've noticed that some gardeners tend to cut conifers back to dead wood, which then can't recover. I did it with one of mine which was in the way of the step leading off the patio, so in the end it had to come down. Perhaps if you leave them untrimmed at the place they are brown, or use them as a frame to grow a vine or creeper over rather than pulling them down. I think they must be like lavender, once you cut past the live wood it won't recover.