2 thoughts - one I'm sure you have already thought of the first.
- spur on the buried dead man part. The spur would catch when the dead man is "set" and prevent it from coming up too far. Just bevel one end and then hammer the beveled point out of alignment.
- TI rod driver - 1/4" diameter TI rod. Available from McMaster-Carr, 12" for $11.89. The TI alloy they have is even harder, but the pure TI is good enough for this. If a longer rod is desired, the 36" length is $30.26 and can be cut down into 2 rods. Seems that 18" would be long enough and 2 people could each get one rod for $15.13 each. The rod I have is 32" and 4.15 oz, so an 18" rod would be approximately 2.3 oz. Maybe heavier than AL tubing, but it will take the hammer treatment better. Would probably want something with a bigger diameter than 1/4" for the buried dead man.
- Stainless Steel tubing - 1/4" diameter. Welded and drawn would work well. I have a piece 14.75", 1.55 oz.
The stainless tubing is lighter and cheaper than the TI rod and strong enough for the driver.