Divers I know mark the spot like that.

They drive over their lump, or find the edge they want, and when they see what they want on the sounder, they toss a marker buoy over.

Next, they go up wind/up current, and drop the pick, allowing enough line out to drift back to where their marker buoy is.

If it doesn't hit it right on the head, they up anchor and try it again.

Zoom your GPS right in and stop straight on the spot then let the boat drift off watching what direction you travel and how far / fast the drift is then drive directly up the snail trail untill you're past the spot far enought to anchor allowing for the depth of water in your estimation so you can hang back over the spot. 

If your GPS doesn't go down far enough use a marker buoy but remember that the buoy will be hanging back from the actual spot due to the tide or wind

Turning your motor once anchored can allow you to swing  the boat across while anchored in a bit of tide and changing the tie up point to one side will make yor boat head over in the other direction for fine tuning.

If you have a good chartplotter and a couple of skills, its not too hard to get close enough to the spot (say 2-5m). You need to be able to zoom your chartplotter in and mark the spot exactly. If you cant find the spot while just driving around, then you've either marked it off a bit from the actual spot (easy to do if you dont account for any backtracking, as your sounder shows a history), or your GPS may not be accurate/quick enough (i've had some painful sessions with some peoples chartplotters). 

On my sounder, I can hover the cursor over the spot and it will tell me the distance and the heading. Then I usually go downwind from the spot, then you want to drive through your spot at the correct angle (using your test drift as carnarvonite said, or just head straight into the breeze). When you're plotter says you've gone the right distance, have your deckie drop the anchor and slowly drift back letting out the line until your plotter says you are exactly over the spot. Again, if you have a good plotter, you should be able to then see exactly how far you are from the spot. If you make a mistake, then pull the pick and move however many meters you need to and you'll be spot on it. If you keep in mind what you did, you can finetune your technique and get spot on most times first go.  Although for berleying, you dont need to be ultra-accurate, and you probably want to be upcurrent of the mark a little anyways.

If you cant find the spot while driving around, you may need to refine your techniques/plotter though. You're unlikely to find the spot while drifting back onto it if you cant find it while driving. So make sure Step 1 is down pat first. Having it accurately marked on your plotter also means you know you're over the spot when you're over it, as it will look quite different while you're just floating over it, rather than moving/drifting/driving over it. 

Although you should really use a good scope (a few times the depth), if its calm and you're on the boat, sometimes a shorter scope will be OK if you can get the anchor to stick.  Running a 5:1 scope in calm weather means you will swing a lot more.

If using a drop marker, you need to make sure you are marking the right spot. E.g. if you're sounders slow, you may see something nice on the sounder, but really its 20m back from the boat. Dropping a marker when the whole feature is on the sounder will mean the marker is off. So you need to be "slicing it in half" on the sounder.

If using a marker, you can tie a short section of strong rope, then tie some thin rope for the main line. Because you'll use a small float, you can use some very thin line like VB cord (or even 100lb mono) so the marker goes relatively vertical. You can rig two floats, one small one (less bouyancy than the weight/anchor), and a larger one. If the smaller one sits underwater, it will keep the line much more vertical, while the second larger buoy will stop it disappearing from view. A few ways you could set this up though.

Takes practise!!!

Some of the blokes i fish with think i get a little too over the top when it comes to lining up a spot, or anchoring on the spot.

But hey, if your not on the spot, your not going to get the fish!!!

I zoom my GPS right in at times when fishing a small lump to 20m and manouver the boat slowly.

Think alot of it comes down to knowing how your boat moves and drifts, once you get this, its much easier.

If there is a bit of a current running keep in mind that your lines are going to hang out behind the boat and if you are directly over the spot your baits are missing it completely so you need to be anchored further upstream from your mark for your baits to be right on the fish.

Thanks guys awesome info there I appreciate the detailed posts and can't wait to try out a few things this weekend!

I'm using a Lowrance HDS5 chartplotter, not sure on the zoom level, but soon will. As for the sounder, great info there cheers hlokk about what I see is actually history. I'll also have a play with the zoom and scroll speeds too.

Cheers!

Is your HDS the combo or do you have seperate units. If it is the combo unit you can mark spots on the sounder that will transfer to the GPS map. Just put the cursor on the spot you want on the Sounder image and press enter a coupla times and you have the exact spot you want. I mark my dive spots like this and get back to them every time. I drop my anchor right on them and then down the anchor rope I go to the spot I marked.

Great thread - thanks for the info