Making an IBH helmet secure

[Someshot]

Hi guys,

Recently bought an IBH replica second hand off the forum, everything seems to be in order. The problem i'm having is keeping it secure, the straps are tight and foam inserts in place. But the helmet seems to lack anything to keep it from moving whilst it's on my head, with a little bit of pressure I can slide it back off my head. Does anyone have any ideas, having had similar problems, as to what I can do to prevent this?

Someshot