I just swim out off there I havnt found a certain spot yet. I cover a lot of ground so I dont think anchoring is a good idea. you could just tow it while diving but I dont know how much drag it is
(I supposed this belongs elsewhere, but I'll let a moderator worry about that.)
If you'll notice when there are kayaks in the water at Venice, most move about as divers tow them via their anchor. That way when you are getting back into the kayak, it stays put for loading goodie bag, scuba, etc. Allows you to take waypoints as well.
Anyway, I tow with a 1 kg claw-style anchor. Very handy for moving about on the bottom, don't need to compensate with added buoyancy. I anchored for about three years, but the long swim back to the kayak was a big pain.
On the other hand, when swells get big, towing can be work. However, it would be even more work then to swim back to an anchored kayak that has drug its hook a 1000 ft. in addition to the 1/4 mile you swam from your anchor point.
However, not that many kayaks have enough weight-bearing capacity (?450 lbs.) for the average size diver, all the kit, and an extra tank. No problem when it is calm, but quite a feat in heavy surf. Likewise, few have below deck stowage for an extra tank.
Plus, take it from me, it isn't as easy as it looks. You will probably want to start off with just one tank. My buddy and I can get 2 hours out of an AL80. Typically, by that time, I'm ready for a surface interval.
In any case, good luck whatever method you decide on.