Thanks for your enquiry.
You have absolutely nothing to worry about if you allow your neighbour to carry out maintenance. Under adverse possession law (ie the law where one party claims another party's land), you have to show that your possession of the said land was WITHOUT the consent of the true owner. So, if you grant consent, there is no "adverse possession".
In any event, a party can't claim another party's land, where that party has a right of way over the land in question!
You are therefore doubly covered, and your neighbour would not be able to make any claim over your land in the future.
I hope this assists and sets out the legal position.