4.2 A mark is set when the jack having been bowled, does not go off the green, is not prevented from going off by resting against anything at the edge or in the channel or, after lawful objection, is proved by measurement, with a certified measure, to be at least 19 metres from the footer, with the footer at least 1 metre from the edge.

References From the Laws Of The Game
D1a The LEADER Is the player who has the first attempt to set a mark and shall deliver the first bowl after any attempt to set a mark.
4.4a Objection to a mark set by the leader can only be made by the leader’s opponent after the first bowl has come to rest. If the opponent objects before the leader’s first bowl has come to rest, the leader may have the jack, and bowl if played, returned to have another attempt at setting a mark. Only the opponent can object to the mark. An opponent objecting to a mark must make a clear indication that an objection has been made.
4.5 If the leader fails to set a mark, the leader’s opponent is then entitled to an attempt at setting a mark. In pairs this will be the player waiting to follow the leader.
4.6 If the leader fails to set a mark, objection to an attempt by the opponent must be made by the leader before delivering the first bowl.
4.7 If the opponent then fails to set a mark, the leader shall have another attempt and so-on, alternately, until a mark has been set by one of them. The original leader to play the first bowl.
5.15 After each end is concluded, the footer shall be placed at the jack by the last player. The footer may only be repositioned by the leader of the next end and before the first attempt to set a mark, anywhere within a space of one metre from where the jack lay at the conclusion of the last end but at least one metre in from the edge of the green. The footer must not be moved after the first attempt to set a mark by either the leader or the opponent until the end is concluded.