I only have a baby 6.0m and do similar when in Paxos - leaving her anchored whilst we go off diving. I can tell you, this really focusses you on underwater navigation skills
. The first year I did it i spent half my dives worrying if she would still be there when I came back !
Most of the locations I anchor in are in sheltered bays or atop rocky pinnacles - one of which has some tricky currents.
I only have a 5kg folding grapple ( less than ideal I know), with 6 m of chain and andwith a good length of warp out, she never moves. The chain is as everyone points out, the key. I do where unsure of the current, wedge the anchor into a convenient crevice if possible, and then liberate on my return.
I use uncalibrated (no windlass) stainless chain - clean, rust free & definitely worth it for your very beautiful new toy.
I dont have a roller fairlead but do have on on the transom so use this to retrieve the anchor as opposed to pulling up over the bows - really saves on scoring the rubbing strake and tubes
Do take time to see how the RIB settles at anchor before jumping in - if only for peace of mind