Dear TLG,

Like Later, Peter said, an old barbell plate works well. So does an old cast dumbell.

If you only need one on occasion you can make a workable anchor out of a heavy plastic jug, like a laundry detergerent jug, filled with wet sand or gravel.

You can also buy a navy fluke style anchor or a mushroom anchor of about 8 pounds pretty cheaply. Don't get the kind that has the flat sharp flukes for diggin in mud, but the kind like Popeye had tattooed on his foreman if you go for a fluke anchor.

Best Wishes,
Avalon