Okay, this is a very common, and very important, situation that comes up in the field. Here's the breakdown, from a veteran perspective

You are 100% correct in that you need an equipment grounding conductor (EGC) run with your new feeder to the pole barn.

There is no safe way around this that adheres to modern electrical code (NEC).

Why It's Not Negotiable (Generally)



Safety

The primary reason for an EGC is safety. In the event of a fault (e.g., a live wire contacting a metal enclosure), the EGC provides a low-impedance path back to the source (the main panel). This allows for a high fault current to flow, tripping the breaker quickly and minimizing the risk of electric shock and fire. Without a properly sized EGC, the fault current could take a longer, more dangerous route back to the source, potentially through people or other unintended paths.

Code Compliance

The National Electrical Code (NEC) has evolved to recognize the importance of a properly sized EGC. Modern installations, almost universally, require a four-wire system (two hots, a neutral, and a ground) for feeders to detached buildings like pole barns. This is true whether the subpanel is in the pole barn or even if you're just feeding something from the pole barn.

Liability

As a licensed electrical contractor, you are responsible for ensuring the installation is safe and meets code. If you proceed with an unsafe or non-compliant installation, you could be held liable for any resulting damages, injuries, or even death.

Why the Existing URD Feed is Likely an Issue



URD and Grounding

While URD can be used for feeders, the fact that it's only three-wire almost certainly means it's not compliant with current codes for feeding a detached structure. Older installations sometimes relied on grounding to the neutral, but this is no longer permitted for separately derived systems like a subpanel in a detached building. This is due to the risk of objectionable neutral current on the ground, and the potential for a lost neutral connection to energize the equipment grounding system.

No Conduit

The fact that it's not in conduit is less of a concern from a grounding perspective, as long as the URD is rated for direct burial (which it likely is). However, if it's exposed to physical damage, that's a separate issue.

Regarding your question of alternatives

There is one exception in the 2020 NEC but I never recommend using it and it requires several other things to be compliant.

Here's the guidance I would give as a veteran Electrical Contractor


Reinforce the Safety Argument

The homeowner needs to understand that this isn't just about code compliance; it's about protecting themselves, their family, and anyone who uses the pole barn. Explain, in simple terms, how the EGC works and the potential dangers of not having one.2.

Document Everything

If the homeowner still refuses to pay for a proper installation, document your conversation and your recommendation in writing. Have them sign a waiver acknowledging that they understand the risks and are instructing you to proceed against your professional advice. However, be prepared to walk away from the job. Protecting yourself and your license is paramount.3.

Consider Alternative Options (if possible)



Smaller Subpanel/Load Reduction

Could the homeowner get by with a smaller subpanel and less load in the pole barn? If so, this might reduce the cost of the new EGC.4.

Stand Your Ground

While it's tempting to try to find a "workaround" to keep the customer happy, the reality is that there are no shortcuts when it comes to electrical safety. You need to stand your ground and insist on a code-compliant installation, even if it means losing the job.5.

Consider referring the job to someone else

It's important to note that other contractors might have different levels of risk tolerance or comfort with certain installations. If you are uncomfortable with the situation, it may be best to refer the job to someone else.

In summary, there is no safe and code-compliant way to add a subpanel to the pole barn without running a properly sized equipment grounding conductor back to the source. The homeowner needs to understand the risks involved, and you need to protect yourself and your license by insisting on a safe and code-compliant installation.

This is not legal advice, consult with a qualified electrical engineer or inspector for specific guidance on your situation. However, this should give you a strong starting point. Good luck! Flag for review