It's a good topic & you've been given some good advice .
I'l give you a tip that should reduce the instances of fouled anchors .
NEVER THROW AN ANCHOR OUT !!!!!!!!!!!
Lower your anchor slowly - once you feel the bottom keep tension on the rope & allow the boat to drift (maintaining tension on the rope) . Once you have let out around 3 X the depth eg 30m in 10m of water & you've tightened up & felt the anchor bite - then tie off .
Chain length - ideally the length of your boat .
Generally speaking most fouled anchors occur when the chain piles on top of the anchor - the above technique avoids this & allows the chain to lay straight & assisting in the bite of the anchor . It takes a little longer this way but it also gives you a greater chance of success . If conditions are a little blowy - keep the motor in gear . lower the anchor as above . .
If I wanted to be accurate on a specific location - I would lower the anchor & lift it slightly .... then once I had my position lower the anchor down those last couple of meters (as above) .
Finally - Save an buy a Minn Kota or Motorguide with spot lock - life becomes so much easier
Chris