Alfie (10 months) is driving me mad at the moment as he's picking up anything he can find at the park.  It's particularly bad lately due to the nice weather as people having picnics leave stuff lying around.  His favourite is any sort of tissue or paper, but in the past fortnight he's found a nappy, sanitary pad, pair of knickers and socks (it is a nice park, honest!).  Plastic is about the only thing he'll leave, unless it's a bottle.  If I see him approching something I'll say very firmly "no!" but he ignores me. 
I can't for the life of me get him to drop whatever he's got.  However nice a treat I have, it's just not enough to make him leave what he has and come to me.  If I
ever manage to tempt him away and give him a treat, how do I know that he doesn't think he's getting the treat for finding something and picking it up, rather than because he's left it alone?
Any advice greatfully received!  Thanks.

Have you actually taught him the leave command.  It might be worth starting at home on items less interesting to him and work your way up.  Unfortunately no quick fix.

I agree teach the leave it command and then teach drop it....I don't care much for the word No cause it is used for so many things.

Good luck :)

I had success with teaching the leave command using this method:

Have a really tasty treat in your hand.  Let him know you have it, but curl your fingers over so he can't reach it.  If he's like most dogs, he'll nose your hand, maybe try to paw at it, and let him do so.  As soon as he turns his nose away (he will eventually) praise him and give him the treat.  Work this in to your normal training schedule and he will get the idea.

I've also found that once my girl's attention is fixated on something (a dead rabbit, say, her favourite!) just shouting her name won't work.  You have to get her attention off the item and on to you.  If I make a really loud noise (a shrill whistle or clapping my hands) she'll look up and see what's going on.  If I then call her to me, she'll ignore the previously exciting object and come back.

Good luck from Hayley and Benson ! :D

my labrador bitch dose this but wen he picks rubbish up tell him of and igroe him for 5
minets or teach him drop/leave it works but takes a long time 
                              hope it goes well
                                                    hilarybrenn

I'd also teach a 'leave' command but not quite like Bennyboo.  'Leave' should mean just that - leave and DO NOT TOUCH, so giving the treat from your hand when you've told him to 'leave' it is counter productive.  I'd put an empty dish on the floor and have a treat in your hand that you know your dog likes.  Take your dog towards the dish (on a lead) and when he goes to investigate the dish say 'leave' and gently encourage him away by letting him smell the treat in your hand and drawing it away from the dish.  When his noses moves away from the dish give him the food from your hand.

Next place a boring bit of food in the dish and repeat the whole exercise.  Keep changing the food in the dish from boring up to the best titbit in the world and repeat the process but NEVER allow your dog to take the food from the bowl.  His reward from your hand is always for LEAVING the tasty morsal in the dish. 

Then try out the command on tissues you've previously wrapped smelly cheese in or anything else you know your dog might be interested in.  When he's pretty much 100% leaving all your deliberate ploys start trying him outside on anything that takes his fancy but make sure you always have a reward in your hand for his good behaviour.  Then start dropping off the frequency of the food reward and start using just verbal praise.