I'll NEVER use a shovel or even a long handled digger (such as a military shovel) in parks. The more you increase the size of the digger, the more the odds are that somebody will get "set off" and decide to complain to the authorities. Think of it as somebody playing music. It reaches a certain point in volume when even the most mild among us will say "I've had enough!" and call the cops. People don't care or think about how good of a job you may do with repairing a hole. They see that shovel, even a small shovel, and it will set some of them off and then it's game over.
The cops, when called, don't care about your rights. 9 times out of 10 they just want to pacify whoever is complaining, and so the easiest way to do that is to ask the "offender" to leave. They don't want their supervisor to find out they've been called back to the same location 30 minutes later because the cop didn't poor water on the situation. Easiest way to erase a problem is to ask the person "offending" to leave. That's why on these cop shows they'll ask somebody to leave in a dispute, even if they haven't got violent, because they just want to shut up the person who is making the effort to call the police station in the first place.
Way I look at it, you've got to bend down to retrieve the target anyway, or probably to repair the hole as best as possible (which means using your hands), so why not just get down on the ground to begin with and get it over with from start to finish. Also, I have read stories of people metal detecting getting charged with brandishing a weapon (yes, shocking, but never the less true...). For that reason alone, I want a small digger held in a harness, and only pull it out and hold it in my hand when I'm on the ground digging a hole. I also stay well clear of people and with my back to them (or the road if nobody is around in case the "fuzz" drives by) just so nobody gets a good view of "the act". You can't reason with people or explain things to them. That would take all day anyway, so the best strategy for me is to avoid conflict whenever possible. Flying under the radar IMHO is the best way to keep the hobby legal in my local parks, but that's just me...
I remember seeing pictures on here a few years back of a guy using a shovel in a local park. The person who posted those pictures said that that was the reason that park was now off limits to any form of metal detecting. It's like pushing your luck with your neighbors. Sure, you'll beg or borrow a tool here or there, but if you get too pushy then they'll cut you off to any more good will in those respects. Got to hedge your bets, is the way I look at it. We may live in the country the some say is still the free-est nation on earth, but in reality we've got no right to dig in parks according to most laws. Never are we going to win that argument. Just aren't enough of us in numbers to sway politicians, so I say "fly by night", so to speak...