I use a folding military shovel with the serrated edge , they work great but you need to dig a hole the size of your coil with the target center or you might hit it and even then be very careful using a shovel. You will still always need to carry a trowl,Fisk makes a very strong plastic one that you can get at Wal-Mart and after some use its strong enough to be sharpened.
But like it's already been said shovels are great for field work and you need something a little more inconspicuous in a park.
And as far as the shovel goes do get a real military shovel, they are made much better and stronger then any aftermarket one I have broken after a couple times out.
HH good luck
red