Well, you can disable this feature by removing your Google account from your phone -- Android phones don't actually require a Google account set up, although they're much more useful with one. I'm not aware of any way to disable remote installation of apps via Google Play.
Your best bet is just securing your Google account. Set up two-factor auth with Google Authenticator and someone will practically need your phone to gain access to your account.
I've never really considered this question -- I'm more worried about someone gaining access to my Google account than I'm worried about my phone. Two-factor auth (Google Authenticator) is the way to go.