Thanks!
There are tracking on my Zumo550, but (maybe because of not enough memory?) it suddenly resets and than its lost.
Dag, looking at the Garmin site it says that your GPS is not 'geocaching friendly'
https://buy.garmin.com/shop/shop.do?pID=414#specsTab/ and so that is why you are having the problem

but one of the GPS loggers will certainly do what you want. I use one when I am out taking photos, I just turn it on and leave it in the saddlebag and just turn it off when I get back. It works really well. Don't forget some mobile phones like the iPhone have GPS built in and there are GPS logging programmes available for them so that may be a cheaper option.