Since your drain is flowing fine I don't think you have an emergency. It is even possible that the hole was created by someone on purpose in order to get access to run a sewer cable down the pipe to unstop it. I have seen that on older plumbing systems with no clean outs. If so, they probably covered it poorly and the covering has become dislodged. Since it is cast iron the depth is probably not a huge problem but the hole in the pipe definitely needs to be protected from soil and debris. I agree that a Fernco (basically a thick rubber sleeve with hose clamps on each end) would be best. You can slit it length-wise and just install it with the split on the other side of the pipe from the hole. It will probably last for years.
Awesome! Thanks for the comments. My blood pressure shot through the roof (which needs to be replaced too) when I found it. I'm glad I can de-prioritize it, once protected. Now, back to electrical work.
If I could only remember to THINK about what I was doing before I did it.
That's why I suggested using a snapper. I merely mentioned that if the pipe was already broken that using a snapper probably won't result in a clean break anyway and you'll have to do some cleanup on the pipe regardless. Whacking an intact length of cast pipe with a hammer obviously isn't the best idea.
I probably should have been more careful in my choice of words. I should have said "if you're going to use cut up soda bottles to patch the pipe, you may as well use materials more appropriate for the work. You're absolutely correct that you can't bury no-hub couplings. When I wrote the response it crossed my mind to point that out, but I kinda moved passed it. My bad. Lazy post, top to bottom.