If you mean stun gun - I would not recommend it. You need to get too close to the dog.

Dogs have a chase instinct. Aggressive dogs are chasing in an aroused state. Anything that causes pain (e.g., pepper spray) CAN make things worse because their first instinct is to fight back.

The second best thing is a VERY loud and authoritative NO!!! yelled in a low voice. If I see that the dog is fixated on my feet - and it's a herding variety of dog (e.g., border collie) I'll stop pedaling because they are likely wanting to nip at my feet (think of cattle.)

The first best thing is to sprint like the crazy, if you think you can outrun the dog.

If the dogs get in front of your bike, you're going to have to dismount. Put your bike between you & the dog(s) and continue to yell "NO" and hope that somebody shows up to corral their little darlings. Just stopping will often take the fun out of it.

Shorter nosed breeds can't run far in the heat. Big dogs can sprint like crazy. Watch their tails - if the tail is up - it's a game. If the tail, ears & head are down they're open for business.