I saw an article in a magazine where the photographer had his model stand in a puddle, he took a shot of her reflection with just the lower half of her legs showing above the reflection. He then got her to step out of her Welly boots while being very careful not to move the boots and proceeded to take a shot of her empty Welly boots. He then merged the two shots to show the portrait reflection in the water but empty boots directly on top of the reflection. It looked good and I thought I would have a go myself but for some reason I cant seem to get a good reflection. I've tried with polarizer without,with flash without. Anyone have any advice on how to achieve this. Setting etc?