Pennies and other small change have always wound up being pierced by the spikes when I've used them.
A brass or stainless steel disc made for the purpose is a better bet and there are lots around. For vibration decoupling and an improved upper midrange, try a Herbie's dot under the disc.
(Steve Herbelin actually sells metal discs with damping pads attached, he calls them Herbie's Grounding Bases, but they cost more than some other devices.)
http://herbiesaudiolab.home.att.net/footers.htm
A brass or stainless steel disc made for the purpose is a better bet and there are lots around. For vibration decoupling and an improved upper midrange, try a Herbie's dot under the disc.
(Steve Herbelin actually sells metal discs with damping pads attached, he calls them Herbie's Grounding Bases, but they cost more than some other devices.)
http://herbiesaudiolab.home.att.net/footers.htm