I use three pennies in the corner under the fringe, and the same in the corner of the under apron. I've found that it does make a difference. Yes, a kilt pin will work on the outer apron, I don't wear them myself though. If you do wear a kilt pin every time you wear a kilt, then you might not need to worry about it, and I'm sure most folks don't. I do it because we get some crazy winds around our place and I've had my under apron on the kilts where I haven't used pennies end up whipping around like no tomorrow. Yes, it's only 3/10 of an ounce or so, but it works for me. As far as the hiding goes, on the under apron, it won't really matter (but you'll be surprised how little they show if you use a wide hem on the apron), and on the over apron, they can be hidden in the fringe rather than tucked in the hem itself.

I've only made eight kilts, so I'm not an expert yet by any means, so if Barb or someone else who knows what they're doing tells me I'm wrong I'll accept it, but it works for me. I discovered this when I made my wife's mini kilt, and it has kept her from showing more than she wanted to, so I have gone back and added pennies to some of my previous creations. It helps, especially for someone like me who doesn't wear a kilt pin.