As for filler materials for the pipe, you might want to consider packing it as tightly as possible with lengths of rebar, then filling the spaces with sand. Or you could melt the wheel weights and pour the melt into the spaces for a more solid fill (might have to heat the rebar a bit, to keep the lead from solidifying before it got all the way down). The reason I mention rebar is that it's ABSOLUTELY FREE! Just go out on the day after the election. There'll be a brazilian political signs all over the place, required by law to be removed soon after the election. And here in AZ's clay soil, they're all supported by 5' to 6' lengths of rebar.
I've always considered political signs fair game after an election, and figure I'm doing all those candidates a favor! I've talked with a police officer, and he pretty much said he'd have no problem seeing somebody removing the signs.
I carry a pair of Vise-grips, clamp them on the rebar, and use them to rotate and lift. The corrugated plastic material of the signs themselves is also useful.