Stand up comics often joke about picking up day laborers lurking around Home improvement stores. There are none found in our community. A local nursery wants $6000 to did a hole and install a few hundred dollars worth of liners and pumps.
(I have done it myself once before. It is just that now I am too old.)
Sometimes high school sports teams will fundraise by offering their services for manual labor. Might be worth a look.
True but, be careful - an established service company carries insurance on their workers should they get hurt on the job. Anyone else would be your responsibility.
Ask people you know. You don’t want strangers coming to your house anyway. If there are landscapers around they probably have laborers available, but the lowest cost will be the friend of a friend who needs a few extra bucks.
Anonymously phone in a tip to the Feds that Jimmy Hoffa is buried there next to Judge Crater.
Put an ad in Craigslist.
How small is this “hole?”
Craigs list look under general labor and part time.
General labor usually has grunt work jobs.
Seriously. What are the dimensions of the hole for this fish pond?
Google grading and hauling in your area, or even a septic tank service.
One guy with a small backhoe can make a decent hole in your yard before lunch. Cheaper and faster than a dozen Home Depot denizens could ever be.
Maybe haggle with the septic tank guy. Most likely he works for himself, and you tell him you’re willing to wait until he’s got a free day or a Saturday, no hurry. That may be your best value.
Go to Home Depot and pick up a couple of guys to dig it. You’ll get it done faster and cheaper than any other option.
Depends how legal you want to be about it. I could go to the 7-11 on my way to work in the morning and pick up a truckload of guys willing to work for $5 an hour.
Yeah, a goldfish pond should be pretty shallow. Maybe 12 to 15 inches deep at the very most? Most of these plastic liners are in that depth range.
Two guys could easily dig it out in a couple hours. Constructing the pond with the liner and other stuff might take awhile just figuring it out. I know you can get a pond kit with everything needed.
I’ve often thought about doing this. I’d really enjoy a Koi pond. But, there’s the maintenance to consider. Keeping it clean. Running a heater in the winter. There’s work involved and no pay. 
As noted in my OP there is no one lurking around our Home Depot at any hour of any day.
LOL, its not always a Home Depot. Do you have any mixed commercial/residential neighborhoods with cheap housing near you? The parking lots in those neighborhoods tend to have a few guys hanging around looking for work (at least in the suburbs).
I asked the manager at my local Mexican restaurant the last time I needed some help with landscaping. Making it clear that it was outdoor work and required some shoveling. He took my number and passed it on to people he knew. I got several calls afterwards.
Seemed safer than just randomly approaching some guys in a parking lot. 
That particular restaurant is run by a Mexican family that came here about 10 years ago.
Do you have a Labor Ready in your town? I’ve never actually used them, but from what I understand they provide day laborers much like what you would find lurking around a Home Depot but provide all the documentation and worker’s comp coverage and such so the arrangement is actually legal. The big drawback is that they cost more and the worker gets less than just hiring someone off the street (literally or not), but they might be worth looking into if you can’t find anything else.
Herndon, at the 7/11.
Do you live on Mars? 
I didn’t know there were Home Depots that didn’t have day laborers somewhere near. The one I go to in San Jose usually has at least a dozen. They hang out right under the big sign that says something like “No soliciting labor… City Ordinance XXXX”.