I am having trouble getting Alfie (15wks) to go into the car, he is traveling in the boot with a dog guard as last week he discovered how to climb over the back seats

but getting him in there is becoming harder, i have tried putting treats down, kong, toys but he tries to jump out immediately I am scared that I am going to trap his legs/ head/tail and that he will hurt himself trying to jump out. When OH is in he holds his lead from the back seats until the boot is shut no problems but it is a nightmare to get him in on my own! We have taken him in the car lots so its not a novelty and as soon as we get going Alfie seems to have no probs with the car just lies down and goes to sleep

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Any ideas about how I can get him in there safely in the first place???