1. The "ground" in question shouldn't be your own property, or tied back to you by paper trail. A trusted ally's property with a handshake agreement, or poorly-trafficked public land. When the Feds decide to make you a target, they can and will use ground-penetrating radar on your property.

2. Regarding the radar, bury the pipes along with plenty of shrapnel to mess with the signature, in the event that your chosen location was not as anonymous as supposed.

3. Use any any all methods to avoid tracking when traveling to/from the location. Eliminate RF signatures from phones, etc, avoid license plate readers and cameras, use bicycles or older vehicles without telemetry collection, wear clothes you wouldn't normally wear and discard afterward, etc.