SendBlockChange issues

Code:java

private Map<Player, ArrayList<Location>> borderBlocks = new HashMap<Player, ArrayList<Location>>();
 
    @SuppressWarnings("deprecation")
    @EventHandler
    public void onDistrictEnter(RegionEnteredEvent e){
        Player p = e.getPlayer();
        ProtectedRegion region = e.getRegion();
        if(DistrictBag.districts.containsKey(UUID.fromString(region.getId()))){
            //get the blocks at the top level of the world and at the borders of the region.
            World world = p.getWorld();
            if(!DistrictBag.getDistrict(region.getId()).getOwner().getPlayer().getUniqueId().toString().equalsIgnoreCase(p.getUniqueId().toString())){
                return;
            }
            if(!borderBlocks.containsKey(p)){
                borderBlocks.put(p, new ArrayList<Location>());
            }
            for(int x = region.getMinimumPoint().getBlockX(); x<= region.getMaximumPoint().getBlockX(); x++){
                borderBlocks.get(p).add(world.getHighestBlockAt(new Location(world, x, 0, region.getMinimumPoint().getBlockZ())).getLocation());
                borderBlocks.get(p).add(world.getHighestBlockAt(new Location(world, x, 0, region.getMaximumPoint().getBlockZ())).getLocation());
            }
            for(int z = region.getMinimumPoint().getBlockZ(); z<= region.getMaximumPoint().getBlockZ(); z++){
                borderBlocks.get(p).add(world.getHighestBlockAt(new Location(world, region.getMinimumPoint().getBlockX(), 0, z)).getLocation());
                borderBlocks.get(p).add(world.getHighestBlockAt(new Location(world, region.getMaximumPoint().getBlockX(), 0, z)).getLocation());
            }
            for(Location loc: borderBlocks.get(p)){
                p.sendBlockChange(new Location(loc.getWorld(), loc.getX(), loc.getY()-1, loc.getZ()), Material.REDSTONE_BLOCK, (byte) 0);
            }
        }
    }
 
    public void onDistrictExit(RegionLeftEvent e){
        Player p = e.getPlayer();
        ProtectedRegion region = e.getRegion();
        if(DistrictBag.districts.containsKey(UUID.fromString(region.getId()))){
            if(borderBlocks.containsKey(p)){
                for(Location loc: borderBlocks.get(p)){
                    Location locc = new Location(loc.getWorld(),loc.getX(),loc.getY(),loc.getZ());
                    p.sendBlockChange(locc, Material.GRASS, (byte) 0);
                }
                borderBlocks.remove(p);
            }
        }
    }

What I am trying to accomplish here is when a player enters their "claim", it outlines it in redstone block, but only for them. That part works.

When the player leaves their claim I want the blocks that were changed to go back to the way they were, but I am having trouble reversing the SendBlockChange.

I have been messing around with this for a few days now, and i'm feeling defeated. Where am I going wrong?

 

Small snippet of mine:

Code:java

 player.sendBlockChange(block.getLocation(), block.getType(), block.getData());

You surround that with a for loop, looping through the blocks in the region.

It sets the block back to its original content, hence block.getType() and block.getData()