There were a number of proposals for the MX (later called Peacekeeper) ICBM deployment, using a variety of strategies to avoid the loss of US second strike capability. One proposal, called 'Racetrack' used a large number of lightly hardened sites, linked by a network of roads and railroads, with the idea being that the Soviets couldn't know where the missiles were at any given time, and would therefore have difficulty targeting them. The other major proposal was 'Dense Pack', where missiles would be stored in deep, very hardened silos close together; the idea being that a Soviet bomb powerful enough to destroy one silo would also destroy the incoming missiles aimed at its neighbours.
Racetrack was implemented by the Carter administration in '79, and cancelled by Reagan in '81; Dense Pack was never implemented, as it was found to be trivially easy to overcome by timing an attack so that the Soviet warheads all arrived within a very short time-frame.
The 'Rail Garrison' concept was a later proposal, and was planned to start in '92; It proposed using the rail network to move missiles around the country in a similar concept to Racetrack, but was cancelled when the Cold War ended in '91.
By the mid '80s, SLBM technology had pretty much rendered land based ICBMs obsolete; Submarines can move about undetected, and can launch from much closer to the target than ICBMs, so once 'third generation' SLBMs were developed that could carry a similar number and size of warhead to land-based missiles, and could be targeted with similar accuracy, they became the better option for both first and second strike capability.
