Case Description

I have had a fence put between our properties since about 1987 to keep my dog in his yard and not out and about.
As of February 2008 I have had to have my left knee replaced so now my new wife has been a bit upset with the fact that I had been still cutting my lawn with a gas powered mower,My property is about 1/3 acre plus or minus.
I purchased a riding mower to eliminate the excessive wear on the artificial knee as my job itself does that well enough.
Before I had my knee replaced I had replaced a run down fence on the other side of my property and in doing so I also replaced the fence that was in between my house and detached garage thinking I had left enough space to allow for any future purchases (riding mower).
I spoke to my neighbour (D) about a month ago in regards to moving my fence as I am damaging my gate between the house and the garage going though it as I did not make the gate/opening large enough.
Last week I spoke to (R) in regards of the same issue in moving my fence between our properties(to the proper surveyed peoperty line) to allow for a larger gate to move the mower to the front yard as well.
As of August 31 2009 when I got home from work I was told by my wife that (D&R) in fact had frantically dug up a large area where the now existing (My fence) is and had planted and is still planting plants and shrubs up to the fence.
Yesterday I had called to go over to re- explain the conversation about moving the fence to put in a gate to access the front yard with the riding mower, (R) was in the middle of dinner and said that we could meet and talk about the fence, I went over as soon as I heard them outside and stated that \"I wish I had caught you sooner than this with all of your plants in as I still need to move the fence over about a foot(property line) to allow the space needed to install a gate to accept the riding mower to do the front yards mine as well as theirs as we do take turns in doing the front yards and in between in the past as a practice that has been done since 1985 when I bought my home.
I was told basically that (R) did not want to argue and stated some law that she can take possesion of said lands due to the fact that she has kept up such lands over the years also that the fence has been in place(I installed 1986-early 1987 before my survey was done in Oct. 1987) after 15 years.
Before this whole episode began her now deceased father (1year) and I had a great neighbourly relationship I would help fix their pool and so forth aide in the removal of an old fuel tank and so on being a good neighbour is what I thought it was all about and to help each other when a where possible!
Now I am in this predicament with my neighbour and the idea of loosing land to this issue as well as being treated so poorly after all of these years.
I went to City Hall in regards to this issue of the fence and the property line, They stated that as far as they can see it is still my property BUT to seek legal advice to get a deeper understading and hopefully closure to this issue as well as does (D&R) have the legal right to make such a bold move and statement to the property line?
In closing do I have the legal right to move my fence to the legal(surveyed) property line?
Any advice in the matter would be greatly appreciated to resolve this issue as well as hopefully salvage a neighbourly relationship again!