Apparatus, comprising: a first rail member including a plurality of first openings spaced apart along a length of the first rail member; a second rail member; at least one vertical support member mounted to and extending between the first rail member and second rail member; and a plurality of vertical cables mounted to and extending between the first rail member and second rail member, wherein a first end of each vertical cable is secured within one of the first openings, characterised in that: the second rail member comprises an outer U-shaped channel defined by an outer web member and an opposed pair of outer leg members, the outer web member defining a plurality of outer openings spaced apart along a length of the outer web member; and an inner U-shaped channel defined by an inner web member and an opposed pair of inner leg members, the inner U-shaped channel mounted within the outer U-shaped channel with open ends of the inner and outer U-shaped channels (30, 32) facing each other, the inner web member having inner openings spaced apart along a length of the inner web member, each inner opening being aligned with the corresponding outer opening formed in the outer web member; whereby a second end of each said vertical cable is secured within opposite aligned inner and outer openings (30, 32) of the second rail member. a first rail member including a plurality of first openings spaced apart along a length of the first rail member; a second rail member; at least one vertical support member mounted to and extending between the first rail member and second rail member; and a plurality of vertical cables mounted to and extending between the first rail member and second rail member, wherein a first end of each vertical cable is secured within one of the first openings, characterised in that: the second rail member comprises an outer U-shaped channel defined by an outer web member and an opposed pair of outer leg members, the outer web member defining a plurality of outer openings spaced apart along a length of the outer web member; and an inner U-shaped channel defined by an inner web member and an opposed pair of inner leg members, the inner U-shaped channel mounted within the outer U-shaped channel with open ends of the inner and outer U-shaped channels (30, 32) facing each other, the inner web member having inner openings spaced apart along a length of the inner web member, each inner opening being aligned with the corresponding outer opening formed in the outer web member; whereby a second end of each said vertical cable is secured within opposite aligned inner and outer openings (30, 32) of the second rail member. the second rail member comprises an outer U-shaped channel defined by an outer web member and an opposed pair of outer leg members, the outer web member defining a plurality of outer openings spaced apart along a length of the outer web member; and an inner U-shaped channel defined by an inner web member and an opposed pair of inner leg members, the inner U-shaped channel mounted within the outer U-shaped channel with open ends of the inner and outer U-shaped channels (30, 32) facing each other, the inner web member having inner openings spaced apart along a length of the inner web member, each inner opening being aligned with the corresponding outer opening formed in the outer web member; whereby a second end of each said vertical cable is secured within opposite aligned inner and outer openings (30, 32) of the second rail member.