i was taught a method using 'derma wax' ...also known as eyebrow plastic, which is just a theatrical wax which you soften and then spread across the eyebrow or desired area. after it can be covered with a matching skin tone colour and some powder to stop any shine. often models with very light coloured eyebrows only need some concealer and foundation and a little powder to block them out, but obviously those with dark hair need the full process to hide them.