The currently feasible method of detecting Earth-mass planets is transit photometry, with detection probability decreasing with a planet's distance from the star. The existence or otherwise of short-period terrestrial planets will tell us much about the planet-formation process, and such planets are likely to be detected first, if they exist. Tidal forces are intense for short-period planets and result in decay of the orbit on a timescale that depends on properties of the star as long as the orbit is circular. However, if an eccentric companion planet exists, orbital eccentricity (e sub(i), where i is the inner orbit) is induced, and the decay timescale depends on properties of the short-period planet, reduced by a factor of the order of 10 super(5)e super(2) sub(i) if it is terrestrial. Here we examine the influence companion planets have on the tidal and dynamical evolution of short-period planets with terrestrial structure, and we show that the relativistic potential of the star is fundamental to their survival.