It's hard to know if your pup will be scared or - once scared - exactly what might have triggered it!
I highly recommend having someone helping you - and if possible play with one dog at a time.
Another thing that helps is for them to watch another dog playing.
So if you have a friend with a pup that gets along with yours. Invite them to play while you hold your pups so they can watch. This might be all it takes - because really it's not all that intuitive what you want them to do with this strange looking contraption that has no scent.
Another option that might is to proceed in stages. Do not turn the equipment on at first. Let them sniff it and get used to it not running. Maybe even leave the pulleys lying around inside where they can get used to them and investigate them at will. (maybe not the main drive because dogs tend to like to chew the power switch off - if left unattended with the unit 😂)
Then move in stages. Play with just the flag/lure and try to get them interested in it. The thing they will be most engaged with at this stage is your attention 😂 but that's fun so that's fine!
You might then tie the lure onto the line and play with them this way. You can even start inside the house at first and then move to yard later.
Then - if you have the room inside or move to the yard - (set up just course but still do not turn it on) string the line & flag through the pulleys and move the line by hand to get their attention and interest in the flag. Praise and reward them for all attention they give the flag. If they want to tear it up - the flags are biodegradable so there's no harm - and it won't harm them if they swallow bits. It's made of maize (corn).
When you've built up to using power - I advise taking one dog at time - but if that is impossible (my dogs could not stand not doing everything together) have someone hold them so they can watch the lure move and feel safe. Move it slowly at first to keep the sudden noises to a minimum.
You might not advance past just letting them watch it for a few sessions.
Ideally one dog will show an interest in chasing the flag. If so let just that one go and praise and encourage them. You know your dogs best. They might both be ready to play. But dogs are jealous so if one will chase, the other will be more interested in doing it too. But if they are too interested in chasing each other - they may quickly forget the flag. So you can use this jealousy for good and let one teach the other!
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