Purdy's Endgame Rules: Rule #1

Rook and Pawn vs. King Endgame Rule #1

The defense draws against any pawn that is not more than one rank beyond the middle of the board (a white pawn on the 5th rank) when the defender's King stands on the queening square and the defender's rook is on the rank next-but one to the queening rank (a defending black rook on the 6th rank - Cheron). IF the pawn is on the rank next-but-one to the queening rank, the defender draws, provided he can safely give check - to do so, the defender should try to get his rook behind the pawn.

Either side to move draws
Philidor 1977

Following the rule above we have:

1...Ra6! 2.e5  Rb6 3.Ra7  Rc6 4.e6  Rc1! (now that the pawn has moved, move your rook to the opponent's back rank to begin the checking procedure.) 5.Kf6  Rf1+ (and Black draws. If the Black rook did not have a check now, then White would win)

Again, the simplest rule is to keep your rook on the rank next-but one to the queening rank, preventing the advance of the enemy King, until the pawn moves onto that rank. After the attacking King has moved then and only then, place your rook on the attacker's back rank and check forever (Cheron).