I also think there can be a tendancy to have several small dogs rather than one or two larger ones. Which then gives the small dogs a pack tendancy. The owners seem to have little regard as to how much damage a pack of small dogs can do. The owner attitude of 'they are just excitable', 'they can't do much damage', is deplorable.
I've had so many attacks on my dogs by packs of JRT's it now causes me to head off at speed in another direction rather than suffer the possible oncoming onslaught. It is really difficult to shake off ten 'they are just excitable' JRT's who are intent on nipping every available part of my dogs they can get at. Even worse when the pack owner does not interveen but says 'just leave them to play they can't do any damage'!
Ha, I've been bitten, both dogs bitten with torn ears and bleeding ankles not too mention the trip to the vet for damage limitation on the poor boys you know what!
No, of course not every small dog owner is bad, bad owners are all over the world with dogs of every shape and size. Its just for me, I get a cold shiver down my spine everytime a see an owner with more than two small dogs. Give me a large black brute running towards me at speed anyday! I can always get up a tree!

Anyone know how high a JRT can jump!