Boertien, 32, and Walker, 33, were amongst the first signings made by Albion boss Paul Peschisolido following the club's promotion to the Football League in 2009.
Defender Boertien had a successful first season at the Pirelli Stadium but this campaign has been frustrating for the former Derby left-back, with injuries and the form of Scott Malone limiting him to just 17 appearances before a groin problem prematurely ended his season in March.
Walker has failed to make a regular impression on the first team since signing for the club. The striker made 37 appearances during his two-year stay, scoring five goals.
Source: PA
Source: PA