Thats why I have the hard rule of not being reachable on holidays and state that upfront. I never take a computer with me and often go to places where there is no reception at all - so I couldn't, even if I wanted.
Clients have to cope with that, thats part of the game.
I live in a rural valley with no mobile phone reception. If people call me when I'm home, they get my voicemail. I do have an internet connection at home, but it's not fast and I rarely use it.
I'm on a computer all day at work, and work hard - when I go home, I have little inclination to then use a computer again, even if it's for leisure or games.
Clients have to cope with that, thats part of the game.